U.S. patent application number 10/481989 was filed with the patent office on 2004-09-23 for processes for the purification of bis(2-hydroxyethyl)terephthalate.
Invention is credited to Inada, Shuji, Sato, Kikuchi.
Application Number | 20040182782 10/481989 |
Document ID | / |
Family ID | 29714337 |
Filed Date | 2004-09-23 |
United States Patent
Application |
20040182782 |
Kind Code |
A1 |
Inada, Shuji ; et
al. |
September 23, 2004 |
Processes for the purification of
bis(2-hydroxyethyl)terephthalate
Abstract
An object of the present invention is to provide a method of
obtaining BHET of high purity efficiently from an EG (ethylene
glycol) solution containing crude BHET
(bis(2-hydroxyethyl)terephthalate), especially a decomposition
product solution obtained by decomposing a polyester containing PET
(polyethylene terephthalate) as a main component, by use of EG,
while minimizing by-production of impurity components such as DEG
(diethylene glycol), DEG ester and oligomers. The present invention
is a method of purifying BHET by subjecting the decomposition
product solution to crystallization and solid-liquid separation
under specific temperature conditions. Further, the present
invention is a method of purifying BHET which comprises evaporation
steps of evaporating low-boiling-point components from the
decomposition product solution under specific conditions so as to
obtain a melt solution and a molecular distillation step of
distilling the obtained melt solution under specific conditions so
as to obtain a specific fraction.
Inventors: |
Inada, Shuji; (Minato-ku,
JP) ; Sato, Kikuchi; (Fukuyama-shi Hiroshima,
JP) |
Correspondence
Address: |
Anderson Kill & Olick
1251 Avenue of the Americas
New York
NY
10020-1182
US
|
Family ID: |
29714337 |
Appl. No.: |
10/481989 |
Filed: |
December 24, 2003 |
PCT Filed: |
May 30, 2003 |
PCT NO: |
PCT/JP03/06878 |
Current U.S.
Class: |
210/634 ;
210/669; 210/702; 210/774; 210/806 |
Current CPC
Class: |
C07C 69/82 20130101;
C07C 67/54 20130101; C07C 67/54 20130101; C07C 67/52 20130101; C07C
67/52 20130101; C07C 69/82 20130101 |
Class at
Publication: |
210/634 ;
210/774; 210/702; 210/669; 210/806 |
International
Class: |
B01D 011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 4, 2002 |
JP |
2002-163221 |
Feb 3, 2003 |
JP |
2003-26123 |
Claims
1. A method of purifying bis(2-hydroxyethyl)terephthalate which
comprises: (1) a crystallization step of cooling an ethylene glycol
solution containing crude bis(2-hydroxyethyl)terephthalate from a
temperature of at least saturation solubility to temperatures
ranging from 15 to 30.degree. C. and keeping the solution within
the temperature range for at least 1 hour, and (2) a solid-liquid
separation step of subjecting a precipitate containing
bis(2-hydroxyethyl)terephthalate as a main component to
solid-liquid separation while keeping the precipitate within a
temperature range of 15 to 30.degree. C. so as to obtain a cake
comprising bis(2-hydroxyethyl)terephthalate as a main
component.
2. The method of claim 1, wherein the total content of solutes in
the ethylene glycol solution containing crude
bis(2-hydroxyethyl)terephthalat- e is 10 to 30 wt %.
3. The method of claim 1, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
containing, as an accessory solute,
2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate in an amount
of 1 to 8 wt % based on all solutes.
4. The method of claim 1, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
containing a gas barrier agent component as an accessory
solute.
5. The method of claim 1, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
having an electric conductivity of 0.2 to 0.6 .mu.S/cm.
6. The method of claim 1, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
obtained by decomposing a polyester containing a polyethylene
terephthalate as a main component by use of ethylene glycol and
then decolorizing and deionizing a decomposition product.
7. The method of claim 6, wherein the polyester containing a
polyethylene terephthalate as a main component is a post-consumer
PET bottle, and at least some of the PET bottles may be colored PET
bottles containing an ultraviolet blocking agent.
8. The method of claim 1, wherein the cooled ethylene glycol
solution containing crude bis(2-hydroxyethyl)terephthalate is kept
within the temperature range of 15 to 30.degree. C. for 1 to 12
hours.
9. The method of claim 1, wherein the precipitate has an average
particle diameter of 40 to 200 .mu.m.
10. The method of claim 1, wherein the precipitate containing
bis(2-hydroxyethyl)terephthalate as a main component is subjected
to solid-liquid separation by use of a filter press using a filter
fabric having an air permeability of 3 to 30
cm.sup.3/min.multidot.cm.sup.2.
11. A method of purifying bis(2-hydroxyethyl)terephthalate which
comprises: (1) evaporation steps comprising: (a) a first
evaporation step of introducing an ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate into a first
evaporator and evaporating low-boiling-point components at a
temperature of 130 to 170.degree. C. and a pressure of 300 to 1,000
Pa so as to obtain a first melt solution having a total content of
ethylene glycol and free diethylene glycol of 3 to 10 wt %, and (b)
a second evaporation step of introducing the first melt solution
into a second evaporator and evaporating low-boiling-point
components at a temperature of 130 to 170.degree. C. and a pressure
of 50 to 250 Pa so as to obtain a second melt solution having a
total content of ethylene glycol and free diethylene glycol of not
higher than 0.45 wt %, and (2) a molecular distillation step of
introducing the second melt solution into a falling-thin-film type
molecular still and distilling the solution at a temperature of 180
to 220.degree. C. and a pressure of not higher than 25 Pa so as to
obtain a fraction containing bis(2-hydroxyethyl)terephthalate as a
main component and having a
2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate content of
not higher than 1.5 wt % and an oligomer content of not higher than
1 wt %.
12. The method of claim 11, wherein the total content of solutes in
the ethylene glycol solution containing crude
bis(2-hydroxyethyl)terephthalat- e is 5 to 85 wt %.
13. The method of claim 11, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
containing, as an accessory solute,
2-hydroxyethyl[2-(2-hydroxyethoxy)eth- yl]terephthalate in an
amount of 1 to 8 wt % based on all solutes.
14. The method of claim 11, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
having an electric conductivity of 0.2 to 0.6 .mu.S/cm.
15. The method of claim 11, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
obtained by decomposing a polyester containing a polyethylene
terephthalate as a main component by use of ethylene glycol and
then decolorizing and deionizing a decomposition product or a
solution resulting from melting a cake obtained by subjecting the
solution to crystallization and separation by filtration.
16. The method of claim 11, wherein the total of the content of
free diethylene glycol in a condensate obtained by cooling the
low-boiling-point components from the evaporation steps and the
content of free diethylene glycol in the second melt solution is 2
wt % or lower of the total of the amounts of the condensate and the
second melt solution.
17. The method of claim 11, wherein the content of the oligomer in
the second melt solution is 15 wt % or lower.
18. The method of claim 11, wherein the weight ratio of the
fraction to a distillation pot residue in the molecular
distillation step is 9:1 to 5:5.
19. The method of claim 11, wherein the low-boiling-point
components evaporated in the first evaporation step are used as at
least a portion of a cooling medium for a condenser in the
molecular distillation step.
20. A method of purifying bis(2-hydroxyethyl)terephthalate which
comprises: (1) a crystallization step of cooling an ethylene glycol
solution containing crude bis(2-hydroxyethyl)terephthalate from a
temperature of at least saturation solubility to temperatures
ranging from 15 to 30.degree. C. and keeping the solution within
the temperature range for at least 1 hour, (2) a solid-liquid
separation step of subjecting a precipitate containing
bis(2-hydroxyethyl)terephthalate as a main component to
solid-liquid separation while keeping the precipitate within a
temperature range of 15 to 30.degree. C. so as to obtain a cake
comprising bis(2-hydroxyethyl)terephthalate as a main component,
(3) evaporation steps comprising: (a) a first evaporation step of
introducing a melt solution of the cake into a first evaporator and
evaporating low-boiling-point components at a temperature of 130 to
170.degree. C. and a pressure of 300 to 1,000 Pa so as to obtain a
first melt solution having a total content of ethylene glycol and
free diethylene glycol of 3 to 10 wt %, and (b) a second
evaporation step of introducing the first melt solution into a
second evaporator and evaporating low-boiling-point components at a
temperature of 130 to 170.degree. C. and a pressure of 50 to 250 Pa
so as to obtain a second melt solution having a total content of
ethylene glycol and free diethylene glycol of not higher than 0.45
wt %, and (4) a molecular distillation step of introducing the
second melt solution into a falling-thin-film type molecular still
and distilling the solution at a temperature of 180 to 220.degree.
C. and a pressure of not higher than 25 Pa so as to obtain a
fraction containing bis(2-hydroxyethyl)terephthalate as a main
component and having a
2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate content of
not higher than 1.5 wt % and an oligomer content of not higher than
1 wt %.
21. The method of claim 20, wherein the total content of solutes in
the ethylene glycol solution containing crude
bis(2-hydroxyethyl)terephthalat- e is 10 to 30 wt %.
22. The method of claim 20, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
containing, as an accessory solute,
2-hydroxyethyl[2-(2-hydroxyethoxy)eth- yl]terephthalate in an
amount of 1 to 8 wt % based on all solutes.
23. The method of claim 20, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
containing a gas barrier agent component as an accessory
solute.
24. The method of claim 20, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
having an electric conductivity of 0.2 to 0.6 .mu.s/cm.
25. The method of claim 20, wherein the ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate is a solution
obtained by decomposing a polyester containing a polyethylene
terephthalate as a main component by use of ethylene glycol and
then decolorizing and deionizing a decomposition product.
26. The method of claim 25, wherein the polyester containing a
polyethylene terephthalate as a main component is a post-consumer
PET bottle, and at least some of the PET bottles may be colored PET
bottles containing an ultraviolet blocking agent.
27. The method of claim 20, wherein the cooled ethylene glycol
solution containing crude bis(2-hydroxyethyl)terephthalate is kept
within the temperature range of 15 to 30.degree. C. for 1 to 12
hours.
28. The method of claim 20, wherein the precipitate has an average
particle diameter of 40 to 200 .mu.m.
29. The method of claim 20, wherein the precipitate containing
bis(2-hydroxyethyl)terephthalate as a main component is subjected
to solid-liquid separation by use of a filter press using a filter
fabric having an air permeability of 3 to 30
cm.sup.3/min.multidot.cm.sup.2.
30. The method of claim 20, wherein the total of the content of
free diethylene glycol in a condensate obtained by cooling the
low-boiling-point components from the evaporation steps and the
content of free diethylene glycol in the second melt solution is 2
wt % or lower of the total of the amounts of the condensate and the
second melt solution.
31. The method of claim 20, wherein the content of the oligomer in
the second melt solution is 15 wt % or lower.
32. The method of claim 20, wherein the weight ratio of the
fraction to a distillation pot residue in the molecular
distillation step is 9:1 to 5:5.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method for purifying
bis(2-hydroxyethyl)terephthalate. More specifically, it relates to
a purification method for obtaining
bis(2-hydroxyethyl)terephthalate of high quality efficiently by
subjecting an ethylene glycol solution of crude
bis(2-hydroxyethyl)terephthalate containing
2-hydroxyethyl[2-(2-hyd- roxyethoxy)ethyl]terephthalate and an
oligomer as impurities to crystallization and/or distillation under
specific conditions.
BACKGROUND ART
[0002] Polyesters, a polyethylene terephthalate (hereinafter may be
abbreviated as "PET") in particular, are used in fields of various
molded articles such as fibers, films and resins. PET is generally
produced by a method of reacting dimethyl terephthalate or
terephthalic acid with ethylene glycol (hereinafter may be
abbreviated as "EG") in the presence of catalysts. In the
production of PET, to satisfy properties required for a particular
application, functional additives such as a stabilizer, a coloring
agent, an antistatic agent and an ultraviolet absorber are added.
Recently in particular, when PET is used in a container for a
beverage, properties such as an ultraviolet blocking property and a
gas barrier property are required depending on the type of the
content so as to maintain quality thereof. As measures for
attaining such properties, measures such as mixing an ultraviolet
absorber or a gas barrier polymer into PET and laminating thin
layers of the polymer so as to form a multilayered container are
taken.
[0003] Meanwhile, disposal of used polyethylene terephthalate
molded articles, polyethylene terephthalate bottles (PET bottles)
in particular, has become a social problem from the viewpoint of
environmental destruction, and recovery and recycle of the bottles
are promoted.
[0004] As a method for recycling the bottles, a so-called material
recycle method has been practically used which comprises the steps
of recovering post-consumer PET bottles, crushing the bottles into
chips or flakes and washing and cleaning the chips or flakes so as
to use them as molding raw materials for other molded articles. As
for PET as molding raw materials obtained by this method, it is
very difficult to prevent foreign materials such as metals, glass
and resins different from PET from mixing into PET or remove the
foreign materials at a low cost. The foreign materials are a
problem since they cause a reduction in production efficiency in
production of other molded articles, deterioration in quality of
product, and an increase in production costs. Further, in the case
of this method, when colored PET bottles are included in the
collected PET bottles, it is expensive to separate the colored
bottles from uncolored bottles, thereby causing an increase in
costs of the molding raw materials. To avoid this, the colored PET
bottles are no longer used, and colored labels are labeled on the
bodies of transparent PET bottles instead. However, this means also
has a problem that the colored labels impair the appearances of the
bottles and increase the costs, whereby the effect of the colored
labels is not satisfactory. Further, in the case of transparent PET
bottles having other polymers contained therein or laminated
thereon so as to be given functionality, it is very difficult to
separate the bottles from other bottles.
[0005] Other methods for recycling PET bottles have also been
studied, and one of the studied methods is a chemical recycle
method. With respect to recycling of the PET bottles by this
method, the present inventors have studied a method for producing
high-purity bis(2-hydroxyethyl)terephthala- te (hereinafter may be
abbreviated as "BHET") by depolymerizing chips or flakes obtained
by crushing collected PET bottles by use of an excess of ethylene
glycol and purifying the obtained decomposition product solution
(depolymerization reaction product solution: EG solution). As a
result, they have found and already proposed that high-purity BHET
can be obtained by purifying the above reaction product solution by
a combination of decolorization, deionization, crystallization,
distillation, and other treatments (refer to Patent Documents 1 to
16).
1 (Patent Document 1) JP-A-2000-53802 (Patent Document 2)
JP-A-2000-169623 (Patent Document 3) JP-A-2000-239233 (Patent
Document 4) JP-A-2001-18224 (Patent Document 5) JP-A-2001-48834
(Patent Document 6) JP-A-2001-48835 (Patent Document 7)
JP-A-2001-48836 (Patent Document 8) JP-A-2001-48837 (Patent
Document 9) JP-A-2001-322967 (Patent Document 10) JP-A-2001-335539
(Patent Document 11) JP-A-2002-121173 (Patent Document 12)
International Publication No. 01/10812 pamphlet (Patent Document
13) International Publication No. 01/19775 pamphlet (Patent
Document 14) International Publication No. 01/29110 pamphlet
(Patent Document 15) International Publication No. 01/56970
pamphlet (Patent Document 16) International Publication No.
02/10117 pamphlet
[0006] (the term "JP-A" as used herein means an unexamined
published Japanese patent application")
[0007] The present inventors have further studied a further
improvement in purification efficiency and a further improvement in
quality in this method. As a result, they have found that impurity
components other than BHET, particularly a diethylene glycol
(hereinafter may be abbreviated as "DEG") and components used so as
to impart functionality cause deterioration in quality of BHET.
Thus, the present inventors have studied keeping the contents of
these components in a product BHET as low as possible.
[0008] Since the DEG component and functionality-imparting
components are contained in starting materials (PET bottles) of
chemical recycle, these components must be removed efficiently with
a side reaction kept from occurring.
[0009] Further, the DEG component is not only by-produced in the
depolymerization step but also produced by dehydration condensation
of EG during purification of the decomposition product solution,
e.g., during deionization of the solution. Further,
2-hydroxyethyl[2-(2-hydroxyethoxy)- ethyl]terephthalate
(hereinafter may be referred to as "DEG ester") produced by an
ester interchange reaction between DEG and BHET also causes
deterioration in the quality of BHET. However, since the
characteristic of the DEG component is very close to that of EG or
BHET, it is very difficult to isolate and remove the DEG component
from a product BHET.
[0010] As a result of studying a method for purifying BHET
efficiently, the present inventors have found that the contents of
the DEG component and functionality-imparting components in a
precipitate can be rendered low depending on crystallization
conditions of the decomposition product solution.
[0011] Further, when BHET containing large amounts of the DEG
component and the functionality-imparting components is subjected
to molecular distillation, it must be allowed that the DEG
component and the functionality-imparting components exist in a
product BHET in large amounts or that the yield of the product is
rendered low. The present inventors have found it effective for
preventing this that removal of the DEG component and
functionality-imparting components or prevention of by-production
of the DEG component and functionality-imparting components is
achieved as much as possible before the molecular distillation
step.
[0012] Further, the present inventors have also found that
crystallization of BHET is affected by the electric conductivity of
the decomposition product solution when BHET is crystallized from
the decomposition product solution and that for increasing the
sizes of crystals of the precipitate so as to facilitate
solid-liquid separation, it is effective to render the electric
conductivity small.
[0013] The present inventors have also found that when BHET is
distilled so as to be purified, a polycondensation reaction
proceeds due to exposure of BHET to high temperatures, and an
oligomer having a polymerization degree of 2 to 20 is
by-produced.
[0014] Thus, an object of the present invention is to provide a
purification method of obtaining high-purity BHET from an EG
solution containing crude BHET, particularly a decomposition
product solution which is obtained by decomposition of a polyester
containing PET as a main component with EG and contains BHET as a
main solute and EG as a main solvent, while minimizing
by-production of impurity components, particularly DEG, DEG ester
and oligomers, during a purification process and by separating
these impurity components efficiently.
[0015] Another object of the present invention is to provide a
method of crystallizing and separating diethylene glycol component
and BHET from a decomposition product solution obtained by
decomposition of a polyester containing PET as a main component
with EG, particularly a solution which is obtained by decomposition
of a polyester containing recovered PET as a main component with EG
and contains BHET as a main solute and EG as a main solvent.
[0016] Another object of the present invention is to provide a
method of crystallizing and separations BHET having a low content
of gas barrier agent component when BHET contains the component
(gas barrier agent component) derived from a gas barrier
polymer.
[0017] Still another object of the present invention is to provide
a method of crystallizing and separating a diethylene glycol
component and BHET by subjecting a decomposition product solution
obtained by decomposition of a polyester containing PET as a main
component with EG, i.e., a solution containing BHET as a main
solute and EG as a main solvent to deionization and crystallization
treatments. Still another object of the present invention is to
provide a method of crystallizing and separating BHET having a
lower content of a gas barrier agent component efficiently when
BHET contains the gas barrier agent component.
[0018] Still another object of the present invention is to provide
a method of separating BHET having a lower content of a diethylene
glycol component efficiently by subjecting an EG solution
containing crude BHET, particularly a decomposition product
solution obtained by decomposition of a polyester containing PET as
a main component with EG, i.e., a solution containing BHET as a
main solute and EG as a main solvent, to solvent removal and
molecular distillation.
[0019] Still another object of the present invention is to provide
a purification method of obtaining high-quality BHET efficiently by
subjecting an EG solution containing crude BHET, particularly a
decomposition product solution obtained by decomposition of a
polyester containing PET as a main component with EG, i.e., a
solution containing BHET as a main solute and EG as a main solvent,
to specific crystallization and solvent removal treatments and
molecular distillation.
[0020] Other objects and advantages of the present invention will
become apparent from the following description.
DISCLOSURE OF THE INVENTION
[0021] According to the present invention, firstly, the above
objects of the present invention are achieved by a method
(hereinafter referred to as "first method") of purifying
bis(2-hydroxyethyl)terephthalate which comprises:
[0022] (1) a crystallization step of cooling an ethylene glycol
solution containing crude bis(2-hydroxyethyl)terephthalate from a
temperature of at least saturation solubility to temperatures
ranging from 15 to 30.degree. C. and keeping the solution within
the temperature range for at least 1 hour, and
[0023] (2) a solid-liquid separation step of subjecting a
precipitate containing bis(2-hydroxyethyl)terephthalate as a main
component to solid-liquid separation while keeping the precipitate
within a temperature range of 15 to 30.degree. C. so as to obtain a
cake comprising bis(2-hydroxyethyl.)terephthalate as a main
component.
[0024] Further, according to the present invention, secondly, the
above objects of the present invention are achieved by a method
(hereinafter referred to as "second method") of purifying
bis(2-hydroxyethyl)terephtha- late which comprises:
[0025] (1) an evaporation step comprising:
[0026] (a) a first evaporation step of introducing an ethylene
glycol solution containing crude bis(2-hydroxyethyl)terephthalate
into a first evaporator and evaporating low-boiling-point
components at a temperature of 130 to 170.degree. C. and a pressure
of 300 to 1,000 Pa so as to obtain a first melt solution having a
total content of ethylene glycol and free diethylene glycol of 3 to
10 wt %, and
[0027] (b) a second evaporation step of introducing the first melt
solution into a second evaporator and evaporating low-boiling-point
components at a temperature of 130 to 170.degree. C. and a pressure
of 50 to 250 Pa so as to obtain a second melt solution having a
total content of ethylene glycol and free diethylene glycol of not
higher than 0.45 wt %, and
[0028] (2) a molecular distillation step of introducing the second
melt solution into a falling-thin-film type molecular still and
distilling the solution at a temperature of 180 to 220.degree. C.
and a pressure of not higher than 25 Pa so as to obtain a fraction
containing bis(2-hydroxyethyl)terephthalate as a main component and
having a 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate
content of not higher than 1.5 wt % and an oligomer content of not
higher than 1 wt %.
[0029] Further, according to the present invention, thirdly, the
above objects of the present invention are achieved by a method
(hereinafter referred to as "third method") of purifying
bis(2-hydroxyethyl)terephthal- ate which comprises:
[0030] (1) a crystallization step of cooling an ethylene glycol
solution containing crude bis(2-hydroxyethyl)terephthalate from a
temperature of at least saturation solubility to temperatures
ranging from 15 to 30.degree. C. and keeping the solution within
the temperature range for at least 1 hour,
[0031] (2) a solid-liquid separation step of subjecting a
precipitate containing bis(2-hydroxyethyl)terephthalate as a main
component to solid-liquid separation while keeping the precipitate
within a temperature range of 15 to 30.degree. C. so as to obtain a
cake comprising bis(2-hydroxyethyl)terephthalate as a main
component,
[0032] (3) an evaporation step comprising:
[0033] (a) a first evaporation step of introducing a melt solution
of the cake into a first evaporator and evaporating
low-boiling-point components at a temperature of 130 to 170.degree.
C. and a pressure of 300 to 1,000 Pa so as to obtain a first melt
solution having a total content of ethylene glycol and free
diethylene glycol of 3 to 10 wt %, and
[0034] (b) a second evaporation step of introducing the first melt
solution into a second evaporator and evaporating low-boiling-point
components at a temperature of 130 to 170.degree. C. and a pressure
of 50 to 250 Pa so as to obtain a second melt solution having a
total content of ethylene glycol and free diethylene glycol of not
higher than 0.45 wt %, and
[0035] (4) a molecular distillation step of introducing the second
melt solution into a falling-thin-film type molecular still and
distilling the solution at a temperature of 180 to 220.degree. C.
and a pressure of not higher than 25 Pa so as to obtain a fraction
containing bis(2-hydroxyethyl)terephthalate as a main component and
having a 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate
content of not higher than 1.5 wt % and an oligomer content of not
higher than 1 wt %.
[0036] Hereinafter, the present invention will be further described
with reference to specific examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a step diagram illustrating a preferred
distillation step (combination of components of distiller) in the
present invention, wherein reference numeral 1 denotes a first
evaporator, 2 a condenser, 3 a melt solution transport pump, 4 a
second evaporator, 5 a condenser, 6 a melt solution transport pump,
7 a condensate reservoir, 8 a molecular still, 9 an internal
condenser, 10 heating means, 11 a product output port, 12 a
distillation pot residue output port, 13 a cooling medium
circulating tank, and 14 a heating medium tank.
BEST MODE FOR CARRYING OUT THE INVENTION
[0038] Firstly, the first method of the present invention will be
described.
[0039] (Starting Material)
[0040] In the first method of the present invention, it is
preferred to use, as an EG solution containing crude BHET which is
a starting material, an ethylene glycol solution (EG solution)
obtained by depolymerizing a terephthalic polyester (PET, in
particular) with an excess of EG and subjecting the polyester to an
impurity-removing treatment during or after the depolymerization or
an EG solution obtained by an esterification reaction between
terephthalic acid and EG (preferably a deionized EG solution).
[0041] That is, as the EG solution containing crude BHET, a
solution obtained by decomposing a polyester containing a
polyethylene terephthalate as a main component with ethylene glycol
and decolorizing and deionizing the decomposed product is
preferably used.
[0042] These EG solutions comprise BHET as a main solute and EG as
a main solvent. In general, they can contain, as impurity
components, at least one component selected from DEG ester (solute
component), an oligomer (solute component), DEG (solvent component)
and the like. Further, the EG solutions can also contain
functionality-imparting components, especially, a gas barrier agent
component (solute component).
[0043] Of these solutions, the former solution obtained by
depolymerizing a terephthalic polyester (PET, in particular) with
an excess of EG and subjecting the polyester to an
impurity-removing treatment during or after the depolymerization is
particularly preferably used. In steps prior to a crystallization
step to be described later, these EG solutions are generally
handled at temperatures at which solutes are not precipitated
(e.g., temperatures higher than 50.degree. C.) and which are not
higher than 100.degree. C., preferably at a temperature of 70 to
90.degree. C.
[0044] Illustrative examples of the above impurity-removing
treatment include a treatment for removing a solid foreign material
(such as filtration under heating), a decolorization treatment with
activated carbon, and a deionization treatment (cation- or
anion-removing treatment) with an ion exchange resin. These foreign
material removing treatment, activated carbon treatment and
deionization treatment are preferably carried out in the order
named. Hence, when the EG solution contains ionized coloring
substances, the coloring substances can be removed by the
deionization treatment. Further, when the EG solution contains
insoluble polymers, the polymers can be removed by filtration under
heating.
[0045] The above terephthalic polyester is preferably a polyester
constituting a PET bottle. As the terephthalic polyester, a
post-consumer colored PET bottle which contains an ultraviolet
shielding agent at least in a portion thereof can be used.
[0046] To say nothing of a homopolymer of PET, the above
terephthalic polyester is exemplified by copolymers of PET, e.g., a
copolyester obtained by copolymerizing a small amount (for example,
not larger than 30 mol %, preferably not larger than 20 mol % based
on all acid components) of at least one of other acid components
such as aromatic dicarboxylic acids, e.g., isophthalic acid,
naphthalenedicarboxylic acid and diphenyldicarboxylic acid,
aliphatic dicarboxylic acids, e.g., sebacic acid and adipic acid,
and alicyclic dicarboxylic acids e.g., cyclohexanedicarboxylic
acid, and other diol components such as 1,4-cyclohexanedimethanol
(hereinafter may be abbreviated as "1,4-CHDM"), trimethylene
glycol, tetramethylene glycol and hexamethylene glycol. Of these,
PET (homopolymer) and copolymers thereof are particularly
preferred. These polyesters may be produced by any method.
[0047] The above terephthalic polyester may contain other polymers
such as a polyethylene isophthalate, a polyethylene naphthalate, a
polybutylene terephthalate, a polymethaxylylene adipamide (Nylon
MXD 6) and a polyglycolic acid in a small amount (for example, not
larger than 40 wt %, preferably not larger than 30 wt %, more
preferably not larger than 20 wt % based on all constitutional
polymers). Further, the above terephthalic polyester may also
contain a catalyst used in a polycondensation reaction of the
polyester (such as an antimony compound or a germanium compound), a
stabilizer (such as a phosphorus compound), and a colorant (such as
phthalocyanine dye, anthraquinone dye, monoazo dye, iron oxide or
carbon black).
[0048] The above terephthalic polyester may also contain a polymer
of a gas barrier layer constituting a multilayered bottle, such as
a polymethaxylylene adipamide (Nylon MXD 6) or a polyglycolic
acid.
[0049] In general, the above terephthalic polyester is decomposed
(depolymerized) by use of an excess of EG. The decomposition
reaction can be carried out by conventionally known methods and
conditions such as methods and conditions which have been
previously proposed by the present inventor, including the method
and conditions described in the above International Publication No.
01/10812 pamphlet.
[0050] To carry out the depolymerization reaction efficiently, it
is preferred that the terephthalic polyester be firstly brought
into contact with a depolymerization agent (preferably a
distillation residue of crude BHET) containing BHET and/or a
condensate thereof (preferably an oligomer with an average
polymerization degree of 1.1 to 10) as a main component at a high
temperature so as to be preliminarily depolymerized
(pre-depolymerized) and the depolymerization (actual
depolymerization) be furthered by use of an excess of EG and a
depolymerization catalyst (e.g., an alkali metal compound) so as to
prepare an EG solution containing crude BHET. As the EG, EG
containing a small amount of other glycols or EG containing crude
EG produced in crystallization and solid-liquid separation of the
above EG solution can be used in addition to purified EG. Further,
the depolymerization catalyst is preferably used in an amount of
0.1 to 0.5 parts by weight, more preferably 0.15 to 0.4 parts by
weight, based on 100 parts by weight of the terephthalic polyester.
Illustrative examples of the depolymerization catalyst include
sodium hydroxide and sodium methylate.
[0051] In the preliminary depolymerization, the ratio of the amount
of the terephthalic polyester to the amount of BHET and/or
condensate thereof is such that BHET and/or condensate thereof
are/is preferably used in an amount of 0.1 to 4.5 parts by weight,
more preferably 0.1 to 2.0 parts by weight, particularly preferably
0.1 to 1.0 parts by weight, per part by weight of the terephthalic
polyester. The temperature of the preliminary depolymerization is
preferably 180 to 290.degree. C., more preferably 190 to
270.degree. C., particularly preferably.200 to 260.degree. C. The
reaction time is preferably 0.1 to 5.0 hours, more preferably 0.3
to 1.5 hours. A decomposition product (preliminary depolymerization
product) obtained by the preliminary depolymerization preferably
has an average polymerization degree of about 2 to 40, more
preferably about 5 to 30.
[0052] The depolymerization reaction (actual depolymerization
reaction) between the preliminary depolymerization product obtained
by the preliminary depolymerization and EG is preferably 170 to
265.degree. C., more preferably 190 to 220.degree. C. The ratio
between the amount of the preliminary depolymerization product and
the amount of EG is such that EG is preferably used in an amount of
0.5 to 8.0 parts by weight, more preferably 2.0 to 7.0 parts by
weight, per part by weight of the preliminary depolymerization
product. When the amount of the preliminary depolymerization
product is too small as compared with the amount of EG, the amount
of BHET produced becomes smaller than saturation solubility to EG,
so that BHET can be obtained only in an amount smaller than a
maximum yield obtained based on a total liquid amount to be
deionized, which is uneconomical. On the other hand, when the
amount of the preliminary depolymerization product is too large as
compared with the amount of EG, an oligomer in BHET increases,
thereby lowering the yield of BHET. Further, when BHET exists
beyond the saturation solubility of EG, BHET is precipitated, so
that deionization cannot be carried out. The depolymerization
reaction time is preferably 0.5 to 5.0 hours, more preferably 0.5
to 2.0 hours. The decomposition product solution obtained by the
depolymerization is constituted by a solute comprising BHET as a
main component and a solvent comprising EG as a main component and
may contain an oligomer having a polymerization degree of 2 to 20,
particularly 2 to 10, in a small amount (for example, not larger
than 20 wt %, particularly not larger than 10 wt %, based on all
solutes).
[0053] Further, when EG is used as the above depolymerization agent
from the beginning, the depolymerization temperature is preferably
170 to 230.degree. C., more preferably 190 to 220.degree. C. The
ratio of the amount of the terephthalic polyester to that of EG at
the time of depolymerization is preferably 1:9 to 3:7. When the
amount of the terephthalic polyester is too small as compared with
that of EG, the amount of BHET produced becomes smaller than
saturation solubility to EG, so that BHET can be obtained only in
an amount smaller than a maximum yield obtained based on a total
liquid amount to be deionized, which is uneconomical. On the other
hand, when the amount of the terephthalic polyester is too large as
compared with that of EG, an oligomer in BHET increases, thereby
lowering the yield of BHET. Further, when BHET exists beyond the
saturation solubility of EG, BHET is precipitated, so that
deionization cannot be carried out.
[0054] The above depolymerization is preferably carried out by
placing a rectification column on a depolymerization reactor and
removing water from the reaction solution to the outside of the
system by distillation. At that time, it is preferable to cause
evaporated ethylene glycol to return to the system. By carrying out
the depolymerization in such a manner, the content of water in the
EG solution to be brought into contact with a cation exchanger can
be reduced, so that a hydrolysis reaction occurring with the
cation-removing treatment can be suppressed. The content of water
in the EG solution to be brought into contact with the cation
exchanger is preferably adjusted to be 0.5 wt % or lower. The water
content is obtained by measuring the EG solution by means of an
MK-SS type Karl Fischer moisture meter manufactured by Kyoto
Electronics Manufacturing Co., Ltd.
[0055] The decomposition product solution obtained by the
depolymerization reaction generally comprises BHET as a main solute
(decomposition product) and EG as a main solvent, contains, as an
accessory solute, DEG ester that is contained in the terephthalic
polyester (PET in particular) which is a raw material or that is
produced by a side reaction upon depolymerization, and can also
contain, as other solute components, an oligomer of BHET and
mono(2-hydroxyethyl)terephthalate (hereinafter may be abbreviated
as "MHET") and, as non-solute components, free DEG caused by a DEG
component contained in the raw material terephthalic polyester and
a DEG component produced by a side reaction upon depolymerization.
Further, when the terephthalic polyester (PET in particular) as a
raw material contains a gas barrier agent, the decomposition
product solution contains a gas barrier agent component, and the
solution can also contain a catalyst used in the depolymerization
(such as an alkali metal compound), a catalyst used in the
polycondensation reaction of the polyester (such as an antimony
compound or a germanium compound), a stabilizer (such as a
phosphorus compound), a colorant (such as phthalocyanine dye,
anthraquinone dye, monoazo dye, iron oxide or carbon black), and
impurity ions derived from various stains which are difficult to
expect.
[0056] The EG solution containing crude BHET in the first method of
the present invention is preferably a solution showing a solid
(solute) content at the time of the impurity-removing treatment or
crystallization treatment of preferably 5 to 40 wt %, more
preferably 10 to 30 wt %, particularly preferably 17 to 23 wt %.
When the solid content of the EG solution obtained by the
depolymerization reaction (decomposition reaction) fails to satisfy
the above range, it is preferable to adjust the solid content by
use of EG.
[0057] It is preferable that the EG solution containing crude BHET
in the first method of the present invention be passed through an
activated carbon layer at a temperature at which the solutes are
not precipitated (e.g., a temperature higher than 50.degree. C.)
and which is not higher than 100.degree. C., preferably a
temperature of 70 to 90.degree. C., before subjected to the
crystallization treatment so as to be decolorized and the EG
solution be further brought into contact with the cation exchanger
and then with anion exchanger so as to reduce the contents of
coloring components, cations and anions.
[0058] The electric conductivity of the EG solution is preferably
adjusted to 0.2 to 0.6 .mu.S/cm, more preferably 0.2 to 0.5
.mu.S/cm, by the above ion exchange treatment. Further, the pH of
the EG solution is preferably 2.5 to 7.0, more preferably 3.0 to
5.0. To render the electric conductivity lower than 0.2 .mu.S/cm,
the duration of the ion exchange treatment must be increased. This
increases the side reaction and makes the pH smaller than 2.5,
i.e., makes the solution closer to the acidic side undesirably.
Meanwhile, when the electric conductivity is higher than 0.6
.mu.S/cm, the growth of precipitated particles in the
crystallization treatment is inhibited. Thus, the precipitated
particles are small, resulting in a decrease in yield in filtration
and a reduction in quality due to residual impurities undesirably.
The electric conductivity can be measured by directly applying an
electric conductivity meter 873CC of FOX BOLO CO., LTD. to the
sample.
[0059] The deionization treatment of the EG solution can be carried
out by, for example, passing the EG solution through a layer of ion
exchangers filled in a column so as to make them contact with each
other. When the above EG solution is a suspension, blockages occur
in the ion-exchanger-filled layer, whereby inadequate passing of
the EG solution or partial flow by passing-resisting spots occurs,
so that a stable deionization treatment is difficult to carry out.
Accordingly, contact of the cation and anion exchangers with the EG
solution is preferably carried out with the EG solution kept at a
temperature which is not higher than the maximum working
temperatures of the ion exchange resins and at which crystals of
BHET are not separated out of the EG solution, after solid
impurities (such as fine particles) of at least 1 .mu.m in size are
removed from the EG solution as required.
[0060] In general, the maximum working temperature of the cation
exchanger is higher than that of the anion exchanger. Thus, it is
preferred that the EG solution be cooled at least to the maximum
working temperature of the anion exchanger after the cation
exchange treatment or the cation and anion exchange treatments be
carried out at the maximum working temperature of the anion
exchanger or a lower temperature. The proportion of cations
contained in ion impurities is generally significantly higher than
that of anions in the impurities. Further, the EG solution after
the cation exchange treatment is significantly shifted to the
acidic side, and this leads to side reactions (an ester interchange
reaction between BHET and DEG and a hydrolysis reaction of BHET) in
the EG solution. Consequently, for the purpose of pH adjustment as
well, the anion exchange treatment is preferably carried out
without allowing a long time to pass after the cation exchange
treatment.
[0061] In the present invention, the EG solution is caused to
contact with the cation exchanger for a residence time of 3 to 30
minutes, preferably 3 to 15 minutes. Further, contact of the
decomposition product solution with the cation exchanger is
preferably carried out at a space velocity of 1 to 12 hr.sup.-1,
more preferably at a space velocity of 4 to 9 hr.sup.-1. When the
residence time is less than 3 minutes, a sufficient cation exchange
treatment cannot be carried out, resulting in production of an
oligomer from BHET by catalysis of residual cations. On the other
hand, when the residence time exceeds 30 minutes, the amount of
BHET converted into DEG ester by the ester interchange reaction
becomes higher than a permissible value undesirably.
[0062] Further, after brought into contact with the cation
exchanger, the EG solution must be in contact with the anion
exchanger over a period ranging from 3 seconds to 10 minutes,
preferably 3 seconds to 5 minutes, more preferably 3 seconds to 3
minutes. Thereby, the above ester interchange reaction and
hydrolysis reaction can be inhibited.
[0063] The cation and anion exchangers can take a general form. For
example, they may take the form of particles, chains or fibers or
may be amorphous. When they are in the form of particles, the
exchangers and the EG solution can be brought into contact with
each other by, for example, filling the exchangers in a column and
passing the above EG solution through the column.
[0064] The cation exchanger is preferably a strongly acidic cation
exchange resin, and the anion exchanger is preferably a mixture of
a weakly basic anion exchange resin and a strongly acidic cation
exchange resin. A cation exchange functional group of the cation
exchange resin may be --SO.sub.3H or --COOH, for example. Further,
as the cation exchange resin, commercially available ones such as
DIAION SKIB, SK104, SK110, SK112 and SK116 (products of MITSUBISHI
CHEMICAL CORPORATION) and AMBERLITE IR120B, IR120BN, IR124 and
200CT (products of Rohm & Haas Co. Ltd.) can be used. In these
commercial products, ion exchange functional groups are generally
stabilized as salts such as sodium salts. Thus, to use these
products, the above salts are generally converted into such acid
groups as described above.
[0065] The anion exchange resin is preferably one having
--NR.sub.2, --NH(C.sub.2H.sub.4NH).sub.nH,
--N.sup.+R.sub.3(OH).sup.- (R: alkyl group) or the like as an anion
exchange functional group. As these anion exchange resins,
commercially available ones such as DIAION WA10, WA20, WA21J and
WA30 (products of MITSUBISHI CHEMICAL CORPORATION) and AMBERLITE
IRA400J, IRA67, IRA96SB and XE583 (products of Rohm & Haas Co.
Ltd.) can be used. Of these commercial products, strongly basic
anion exchange resins have ion exchange functional groups which are
generally stabilized as groups having not hydroxide ions OH.sup.-
but halogen anions. Thus, to use these strongly basic anion
exchange resins, the ion exchange functional groups are generally
converted into groups having hydroxyl group anions as described
above. Of these, a weakly basic anion exchange resin having a
primary, secondary or tertiary amine as an exchange functional
group is preferred.
[0066] The above primary, secondary and tertiary amine type anion
exchange resins have ion exchangeable --N.sup.+R.sub.3(OH).sup.-
for the first time when they become neutral or acidic (preferably
acidic). Thus, it is preferable to use the resins in the form of a
mixed bed of the weakly basic anion exchange resin and a strongly
acidic cation exchange resin. The mixing ratio (volume ratio) of
the weakly basic anion exchange resin to the strongly acidic cation
exchange resin is 1:3 to 5:1, preferably 1:2 to 3:1.
[0067] In the above anion exchange treatment, the EG solution is in
contact with the anion exchanger for a residence time of 3 to 60
minutes, preferably 3 to 40 minutes. Further, contact of the EG
solution with the anion exchanger is preferably carried out at a
space velocity of 0.5 to 10 hr.sup.-1, more preferably at a space
velocity of 1 to 8 hr.sup.-1.
[0068] In the first method of the present invention, it is
preferable to confirm that the ion exchange treatment of the EG
solution is appropriate, by measuring the electric conductivity and
pH of the EG solution and checking whether these properties are
within the above ranges. When it is determined that the treatment
is inappropriate, it is preferable to carry out the ion exchange
treatment again. The content of DEG ester in the EG solution (to be
subjected to the crystallization treatment) after the ion exchange
treatment is preferably not higher than 8 wt %, more preferably 1
to 8 wt %, particularly preferably 1 to 6 wt %, based on all
solutes.
[0069] (Crystallization Step)
[0070] The EG solution containing crude BHET in the first method of
the present invention is heated to a temperature of at least
saturation solubility (preferably 50 to 100.degree. C., more
preferably 70 to 90.degree. C.) so as to dissolve solutes
completely, cooled to temperatures ranging from 15 to 30.degree.
C., preferably 15 to 27.degree. C., and retained in the temperature
range for at least 1 hour, preferably 1 to 12 hours, more
preferably 2 to 10 hours, particularly preferably 3 to 8 hours so
as to precipitate BHET such that the precipitate has an average
particle diameter of 40 to 200 .mu.m (measured by use of SALD-200V
ER of Shimadzu Corporation with the solution diluted to 10 times by
EG).
[0071] For example, it is preferable that the EG solution be cooled
from a temperature of at least saturation solubility to a given
temperature within the range of 15 to 30.degree. C. and kept at the
temperature for a given time. After the EG solution is cooled to
the given temperature, the temperature of the EG solution may be
somewhat increased or decreased within the temperature range of 15
to 30.degree. C. Counting of the given time starts when the
temperature of the EG solution reaches 30.degree. C.
[0072] By keeping the temperature of the EG solution within the
temperature range, the content of a DEG component in the
precipitate can be reduced. When the temperature of the EG solution
is lower than 15.degree. C., the amount of precipitated DEG ester
increases, while when it is higher than 30.degree. C., the
solubility of BHET increases, thereby causing a reduction in yield
in the crystallization treatment undesirably.
[0073] When the EG solution is cooled from a temperature of at
least saturation solubility by batch crystallization, the solution
is preferably cooled slowly at a cooling rate of 0.1 to 0.5.degree.
C./min, preferably 0.1 to 0.3.degree. C./min. With the cooling
rate, excessive cooling only in a portion of the solution can be
prevented, and the content of the DEG component in the precipitate
can be reduced. Meanwhile, in the case of continuous
crystallization, it is preferable that an EG solution containing
crude BHET of at least saturation solubility be added to and mixed
with an EG solution which has been cooled to temperatures ranging
from 15 to 30.degree. C. in advance and containing a precipitate
and the mixed solution be then cooled.
[0074] In the first method of the present invention, by cooling the
above ion-exchanged EG solution and keeping the solution at
temperatures ranging from 15 to 30.degree. C., preferably 15 to
27.degree. C., crystals of BHET are grown, thereby facilitating
solid-liquid separation. As the crystallization temperature lowers,
the content of solids in a filtrate decreases and the amount of a
cake to be crystallized increases. However, since the EG solution
contains DEG ester and, in some cases, a gas barrier agent
component, lowering the crystallization temperature causes a
problem that crystallization of the DEG ester and gas barrier agent
component also proceeds along with crystallization of BHET, thereby
lowering the purity of BHET in the cake.
[0075] Meanwhile, an increase in the crystallization temperature
causes a problem that the crystallization of BHET does not proceed
and the solubility of BHET increases, whereby a target yield cannot
be attained. Temperature optimization according to the properties
of the EG solution is required.
[0076] By the crystallization treatment in the first method of the
present invention, the sizes of precipitated BHET crystals can be
adjusted so that they can be filtered efficiently, and the
crystallization of the DEG ester and gas barrier agent component
can be minimized. Consequently, in solid-liquid separation after
the crystallization, the DEG ester, free DEG and the gas barrier
agent component can be left primarily in the filtrate, and the
contents of the DEG ester and gas barrier agent component in a
filtered cake can be reduced. Further, by the crystallization
treatment, coloring substances remaining in the starting material
can be separated from the precipitated BHET crystals.
[0077] (Solid-Liquid Separation Step)
[0078] In the first method of the present invention, solid-liquid
separation following the crystallization treatment is carried out
with a temperature at the time of the crystallization treatment,
i.e., a temperature within a range of 15 to 30.degree. C.
maintained. The precipitate after the crystallization treatment is
preferably subjected to the solid-liquid separation by a filtration
method. Further, the precipitate is preferably filtered out by
means of a filter press using a filter fabric having an air
permeability of 3 to 30 cm.sup.3/min.multidot.cm.sup.2. When the
air permeability of the filter fabric is smaller than 3
cm.sup.3/min.multidot.cm.sup.2, the fabric is liable to have
clogging, thereby lowering processing efficiency. Further, the
content of a liquid in the filtered cake increases, and impurities
in the cake increase. Meanwhile, when the air permeability is
larger than 30 cm.sup.3/min.multidot.cm.sup.2, the meshes of the
filter fabric are so large that fine particles are fallen into the
filtrate undesirably. By the filtration treatment, a filtered cake
having a solid content of 40 to 85 wt %, particularly 50 to 80 wt
%, can be obtained.
[0079] When the precipitate (e.g., the filtered cake) having
undergone solid-liquid separation in the first method of the
present invention is further subjected to a distillation step, it
can be used as a raw material for producing a high-quality
polyester again. According to the results of studies made by the
present inventors, the distillation efficiency and product quality
of BHET is affected by impurities (such as DEG ester) contained in
the raw material to be subjected to the distillation step. Thus, by
subjecting a raw material which is the precipitate obtained in the
first method of the present invention and contains small amounts of
impurities, particularly DEG ester and a gas barrier agent
component, to the distillation step, the desired objects can be
achieved.
[0080] Next, the second method of the present invention will be
described.
[0081] (Starting Material)
[0082] An EG solution containing crude BHET which is a starting
material in the second method of the present invention is not
particularly limited as long as the solution has crude BHET which
is a solute (solid) dissolved in EG which is a solvent in an amount
of 5 to 85 wt %, preferably 10 to 80 wt %, based on the total
weight of the solution. Further, the EG solution containing crude
BHET includes the EG solution used as the starting material in the
above first method and also includes a solution obtained by
subjecting the EG solution to a concentration treatment or
crystallization treatment (preferably the crystallization treatment
in the first method) and then melting a cake separated from the EG
solution by filtration, i.e., an EG solution having crude BHET
dissolved in EG in an amount of 40 to 85 wt %, preferably 50 to 80
wt %, based on the total weight of the solution. More specifically,
when the starting material is a solution other than a concentrated
solution or a filtered cake, the amount of crude BHET is preferably
5 to 40 wt %, more preferably 10 to 40 wt %. Meanwhile, when the
starting material is a concentrated solution or a filtered cake,
the amount of crude BHET is preferably 40 to 85 wt %, more
preferably 50 to 80 wt %.
[0083] To the EG solution containing crude BHET which is the
starting material in the second method of the present invention,
descriptions of the EG solution used as the starting material in
the first method and the filtered cake obtained in the first method
other than a description of the solid (solute) content can be
directly applied.
[0084] Therefore, it is to be understood that what has been
described with respect to the starting material of the first method
is basically included in a description of the starting material of
the second method.
[0085] To be more specific about the above EG solution as the
starting material, it contains crude BHET as a solute and EG as a
solvent. Although crude BHET which is a solute most preferably
comprise BHET alone, it generally contains, in addition to BHET, at
least one solute such as MHET, 1,4-CHDM,
bis(2-hydroxyethyl)isophthalate (hereinafter may be abbreviated as
"BHEI"), DEG ester or an oligomer (polymerization degree: 2 to 20).
Further, the crude BHET preferably contains no gas barrier agent
component.
[0086] Further, BHET preferably constitutes at least 70 wt %, more
preferably at least 80 wt % of the crude BHET from the viewpoint of
an improvement in recovery rate of BHET. Further, the content of
DEG ester as an impurity component in the crude BHET is not higher
than 8 wt %, preferably 1 to 8 wt %, more preferably 1 to 6 wt %.
When the content of the DEG ester is higher than 8 wt %, BHET of
target quality cannot be obtained at the time of purification by
distillation undesirably. Similarly, the content of an oligomer as
an impurity component is preferably not higher than 15 wt %, more
preferably not higher than 10 wt %. When the content of the
oligomer in the starting material is higher than 15 wt %, BHET of
target quality cannot be obtained at the time of purification by
distillation undesirably. Further, it is needless to say that the
total content of these impurity components and BHET does not exceed
100 wt %.
[0087] The solvent most preferably comprises EG alone. In general,
however, it contains, in addition to EG, at least one impurity
component such as free DEG or water. The content of EG in the
solvent is preferably not lower than 95 wt %, more preferably not
lower than 98 wt %. When the content of the EG is lower than 95 wt
%, side reactions caused by impurity components other than EG are
liable to occur undesirably. Further, the content of free DEG in
the solvent is preferably not higher than 3 wt %, more preferably
not higher than 2 wt %. When the content of the free DEG is higher
than 3 wt %, DEG ester is liable to be produced by a side reaction
undesirably.
[0088] (Distillation Step)
[0089] An evaporation step in the second method of the present
invention comprises a first evaporation step and a second
evaporation step. The first evaporation step is a step of
evaporating low-boiling-point components (EG, water, free DEG, and
the like) in the starting material by use of a first evaporator so
as to obtain a first melt solution. The second evaporation step is
a step of evaporating low-boiling-point components (EG, free DEG,
and the like) in the first melt solution by use of a second
evaporator so as to obtain a second melt solution. The
low-boiling-point components refer to components (compounds) having
a lower boiling point than BHET, such as water, EG and free DEG. An
EG solution to be supplied to the first evaporation step is
preferably heated at temperatures at which solutes are not
precipitated (e.g., temperatures higher than 50.degree. C.) and
which are not higher than 100.degree. C., preferably temperatures
ranging from 70 to 90.degree. C., when the amount of crude BHET is
5 to 40 wt %,. Meanwhile, when the amount of crude BHET is 40 to 85
wt %, the EG solution is preferably heated at temperatures at which
crude BHET is molten but side reactions hardly occur, i.e.,
120.degree. C. or lower, more preferably 70 to 120.degree. C.,
particularly preferably 80 to 120.degree. C.
[0090] These first and second evaporators are preferably an
evaporator (i.e., a falling-thin-film type evaporator) having
heating means for evaporating low-boiling-point components (EG,
free DEG, and the like) while causing the starting material or melt
solution to fall in the form of a film. This device has an
advantage that the low-boiling-point components can be evaporated
merely by exposing the solution to high temperatures for a short
time (that is, with a short thermal history). Thereby,
by-production of DEG from EG can be suppressed. Further, these
evaporators also have vacuum means capable of vacuum
evaporation.
[0091] (First Evaporation Step)
[0092] The first evaporation step in the second method of the
present invention is preferably carried out at a temperature of 130
to 170.degree. C., preferably 140 to 160.degree. C., and a pressure
of 300 to 1,000 Pa, preferably 300 to 700 Pa. The temperature is
the temperature of a heating surface, and the pressure is pressure
near the heating surface. When the first evaporation treatment is
carried out at a temperature lower than 130.degree. C., it takes a
long time to evaporate low-boiling-point components (EG, free DEG,
and the like) to preferred concentrations, so that production of an
oligomer from BHET proceeds undesirably. Meanwhile, when the first
evaporation treatment is carried out at a temperature higher than
170.degree. C., DEG is by-produced from EG by a thermal history due
to the high temperature, and DEG ester is further by-produced by a
reaction between DEG and BHET undesirably. Further, when the first
evaporation treatment is carried out at a pressure lower than 300
Pa, solutes (such as BHET) entrain evaporating low-boiling-point
components (EG, free DEG, and the like) undesirably. Meanwhile,
when the first evaporation treatment is carried out at a pressure
higher than 1,000 Pa, it takes a long time to evaporate
low-boiling-point components (EG, free DEG, and the like) to
preferred concentrations, so that production of an oligomer from
BHET proceeds undesirably. If one of the temperature and the
pressure is out of the above ranges, an undesirable result is
produced.
[0093] In the first evaporation step, the solvents (EG, water, DEG,
and the like) are evaporated such that the total content of EG and
free DEG in the first melt solution obtained is 3 to 10 wt %,
preferably 3 to 6 wt %. This treatment time (time in which the
solution is in contact with the heating means) is preferably 1
second to 2 minutes, more preferably 1 second to 1 minute.
[0094] The solvents distilled off by this treatment are cooled into
a condensate by means of a condenser. The condensate can be
directly subjected to a distillation purification treatment
(re-purification treatment) so as to be used as solvents again. In
the present invention, however, it is preferable that the
condensate be used as at least a portion of a cooling medium used
in an internal condenser of a molecular still before subjected to
the above treatment so as to reduce energy consumption. The
temperature of the condensate is preferably 20 to 80.degree. C.,
more preferably 30 to 50.degree. C.
[0095] (Second Evaporation Step)
[0096] In the second evaporation step in the second method of the
present invention, low-boiling-point components (EG, free DEG, and
the like) which could not be evaporated by means of the first
evaporator and remain in the first melt solution are evaporated.
The second evaporation step is carried out at a temperature of 130
to 170.degree. C., preferably 140 to 160.degree. C., and a pressure
of 50 to 250 Pa, preferably 50 to 150 Pa. The temperature is the
temperature of a heating surface, and the pressure is pressure near
the heating surface. When the second evaporation treatment is
carried out at a temperature lower than 130.degree. C., it takes a
long time to evaporate low-boiling-point components (EG, free DEG,
and the like) to preferred concentrations, so that production of an
oligomer from BHET proceeds undesirably. Meanwhile, when the second
evaporation treatment is carried out at a temperature higher than
170.degree. C., free DEG is by-produced from EG by a thermal
history due to the high temperature, and DEG ester is further
by-produced by a reaction between free DEG and BHET undesirably.
Further, when the second evaporation treatment is carried out at a
pressure lower than 50 Pa, solutes (such as BHET) entrain
evaporating low-boiling-point components (EG, free DEG, and the
like) undesirably. Meanwhile, when the second evaporation treatment
is carried out at a pressure higher than 250 Pa, it takes a long
time to evaporate low-boiling-point components (EG, free DEG, and
the like) to preferred concentrations, so that production of an
oligomer from BHET proceeds undesirably. If one of the temperature
and the pressure is out of the above ranges, an undesirable result
is produced.
[0097] In the second evaporator, the low-boiling-point components
are evaporated such that the total content of EG and free DEG
contained in the second melt solution obtained is not higher than
0.45 wt %, preferably not higher than 0.40 wt %. When the total
content of EG and free DEG in the second melt solution is higher
than 0.45 wt %, side reactions such as by-production of DEG and
by-production of DEG ester caused by by-produced DEG are liable to
occur in the molecular distillation step. The treatment time (time
in which the solution is in contact with the heating means) in this
step is preferably 1 second to 2 minutes, more preferably 1 second
to 1 minute.
[0098] The total of the content of free DEG in the first and second
condensates evaporated and cooled in the evaporation steps and the
content of free DEG in the second melt solution obtained in the
evaporation steps is preferably not higher than 2 wt % based on the
total. amount of the condensates and the second melt solution. In
the present invention, production of free DEG can be suppressed and
production of DEG ester caused by free DEG can also be suppressed
in the evaporation steps. Thus, the content of DEG ester in
purified BHET can be rendered low.
[0099] Further, the content of an oligomer in the second melt
solution is preferably not higher than 15 wt %. That is, in the
present invention, production of an oligomer is suppressed in the
evaporation steps. As a result, the recovery rate of purified BHET
can be increased.
[0100] The evaporation step in the second method of the present
invention is characterized in that an evaporation operation is
performed in two steps. When the evaporation operation is performed
only in a single step, the following disadvantages result. That is,
if the concentration of solvent in the crude BHET molten solution
is to be adjusted to 0.45 wt % or lower only in a single step, the
solution must be exposed to harsh evaporation conditions (e.g.,
temperatures higher than 170.degree. C.), and the amounts of
by-produced DEG and a by-produced oligomer become larger than those
in the present invention. Further, the size of an evaporator
becomes so large that the single-step evaporation operation lacks
industrial productivity of BHET in terms of costs.
[0101] (Molecular Distillation Step)
[0102] The molecular distillation step in the second method of the
present invention is a step of subjecting the second melt solution
obtained in the above evaporation steps to molecular distillation.
The molecular still is a falling-thin-film type molecular still
comprising heating means for evaporating a portion of the melt
solution while causing the melt solution to fall in the form of a
film and an internal condenser which condenses a solute (fraction)
evaporated (gasified) by the heating means in a short path.
[0103] Further, the molecular still is preferably allowed to use
the condensate of the solvents evaporated in the evaporation steps
as at least a portion of a cooling medium of the internal
condenser. As described above, the condensate is preferably cooled
to a temperature of 20 to 80.degree. C., more preferably 30 to
50.degree. C. Thereby, the temperature of the cooling medium after
mixed with the condensate can be lowered. The BHET condensation
temperature of the internal condenser is preferably 115 to
125.degree. C. Further, to condense BHET evaporated by the above
heating means in a short path, the distance between the heating
surface of the heating means and the cooling surface of the
internal condenser should be kept equal to or lower than the
average free path of evaporated BHET.
[0104] Distillation by the molecular still in the second method of
the present invention is carried out at a temperature of 180 to
220.degree. C., preferably 185 to 205.degree. C., and a pressure of
not higher than 25 Pa, preferably not higher than 15 Pa. The
temperature is the temperature of the heating surface, and the
pressure is pressure near the heating surface. When the molecular
distillation treatment is carried out at a temperature lower than
180.degree. C., target BHET does not evaporate undesirably.
Meanwhile, when the molecular distillation treatment is carried out
at a temperature higher than 220.degree. C., DEG ester is
by-produced by a reaction between a trace amount of free DEG
produced by a thermal history due to the high temperature and BHET
undesirably. Further, when the molecular distillation treatment is
carried out at a pressure higher than 25 Pa, target BHET flows
toward a distillation pot residue before condensed by the internal
condenser undesirably, even if the BHET is evaporated. If one of
the temperature and the pressure is out of the above ranges, an
undesirable result is produced. Time required for this treatment
(time in which crude BHET is in contact with the heating means) is
preferably 1 second to 1 minute, more preferably 1 second to 50
seconds.
[0105] In the molecular still, it is desirable that not all BHET
contained in the second melt solution subjected to this
distillation treatment be evaporated and BHET be evaporated such
that the weight ratio of the fraction to the distillation pot
residue be preferably 9:1 to 5:5, more preferably 8:2 to 6:4. For
example, when the content of BHET in the second melt solution is 80
to 90 wt %, the weight ratio of the fraction to the distillation
pot residue may be 7:3, for example. Thus, by-produced DEG ester
whose properties are similar to those of BHET can be caused to
remain in the distillation pot residue together with BHET, and a
fraction of higher quality, that is, a fraction having a DEG ester
content of not higher than 1.5 wt % and an oligomer content of not
higher than 1 wt % in the fraction, can be obtained. However, when
the required properties of a product are less stringent, the yield
can be improved by further increasing the evaporation rate of the
fraction.
[0106] The distillation pot residue produced in the molecular
distillation step contains BHET as a main component. Hence, when it
is introduced as a raw material for the above depolymerization of a
polyester, it can be used to promote initial depolymerization.
[0107] In the above molecular distillation step, as described
above, it is preferable to use the condensates obtained in the
evaporation steps as at least a portion of the cooling medium for
the internal condenser. This treatment will be more specifically
described hereinafter. The condensates are subjected to a
distillation purification treatment (re-purification treatment) so
as to be reused as solvents. However, when the condensates are used
as the cooling medium for the internal condenser before subjected
to this treatment, the condensates are heated by the evaporation
latent heat of steam of BHET and are at elevated temperatures when
discharged from the internal condenser. This elevation of the
temperatures of the condensates leads to omission of a part of a
preheating treatment when the condensates are purified by
distillation and contributes to a reduction in energy consumption.
Further, the amount of a cooling medium which is newly prepared and
used as the cooling medium for the internal condenser can be
reduced.
[0108] (Distillation Step Diagram)
[0109] The method for purifying bis(2 -hydroxyethyl)terephthalate
in the second method of the present invention will be further
described with reference to the drawings. FIG. 1 is a diagram
showing a preferred distillation step (a combination of evaporators
and a molecular still). In FIG. 1, reference numeral 1 denotes a
first evaporator, 2 a condenser, 3 a melt solution transport pump,
4 a second evaporator, 5 a condenser, 6 a melt solution transport
pump, 7 a condensate reservoir, 8 a molecular still, 9 an internal
condenser, 10 heating means, 11 a product output port, 12 a
distillation pot residue output port, 13 a cooling medium
circulating tank, and 14 a heating medium tank. The condensers 2
and 5 may be disposed inside or outside the apparatuses. Further,
the first evaporator, the second evaporator and the molecular still
are connected to vacuum means (not shown) so as to render the
insides of the apparatuses vacuum.
[0110] In FIG. 1, the first evaporator 1 and the second evaporator
4 are falling-thin-film type evaporators. A starting material (EG
solution) is fed to the first evaporator 1, low-boiling-point
components (EG, water, free DEG, and the like) evaporated in the
apparatus by heating are cooled so as to be condensed into a first
condensate in the condenser 2, and the first condensate is reserved
in the condensate reservoir 7. A first melt solution is fed to the
second evaporator 4 by means of the melt solution transport pump 3,
low-boiling-point components (EG, free DEG, and the like)
evaporated in the apparatus by heating are cooled so as to be
condensed into a second condensate in the condenser 5, and the
second condensate is fed to a distillation purification system.
[0111] The second melt solution is fed to the molecular still 8 by
means of the melt solution transport pump 6, a fraction is
evaporated by the heating means 10 in the apparatus 8, and the
evaporated fraction is cooled in the internal condenser 9. The
fraction cooled in the internal condenser 9 is taken out as
products from the product output port 11. A residue other than the
fraction is taken out from the distillation pot residue output port
12.
[0112] In a preferred embodiment, the condensate from the
evaporation steps which is reserved in the condensate reservoir 7
is mixed with a cooling medium from the cooling medium circulating
tank 13 so as to be used for cooling in the internal condenser 9,
and the (temperature-raised) cooling medium discharged from the
condenser 9 is returned to the cooling medium circulating tank 13,
and an amount corresponding to the amount of the mixed condensate
is separated therefrom. The separated liquid may be fed to the
distillation purification treatment (recovery purification) system
or may be fed to the heating medium tank 14 which supplies a
heating medium to the heating means 10 of the molecular still 8.
The heating medium is heated to a desired temperature in the
heating medium tank 14. Further, a high-temperature liquid produced
in the distillation purification treatment (recovery purification)
system may be fed to the heating medium tank 14 and used as a
heating medium. Thereby, energy consumption in the distillation
method using the evaporators and the molecular still in a
multistage manner can be reduced.
[0113] Next, the third method of the present invention will be
described.
[0114] The third method of the present invention is a combination
of the above first and second methods. Thus, a description of the
third method is basically the same as those of the first and second
methods. Hereinafter, the third method will be described briefly,
although it is deemed that some characteristics thereof have
already been described with respect to the first and second
methods.
[0115] (Starting Material)
[0116] In the third method of the present invention, an EG solution
containing crude BHET which is a starting material is the same as
the starting material used in the first method of the present
invention. Therefore, this EG solution is preferably a solution
obtained by depolymerizing a terephthalic polyester with EG and
subjecting the polyester to an impurity-removing treatment during
or after the depolymerization or a solution obtained by an
esterification reaction between terephthalic acid and EG
(preferably a deionized solution). These solutions can be prepared
in accordance with the method described above with respect to the
first method of the present invention. An EG solution containing
crude BHET which is obtained by the method is subjected to a
crystallization step.
[0117] (Crystallization Step)
[0118] The EG solution containing crude BHET in the third method of
the present invention is subjected to the crystallization step in
accordance with the method described with respect to the first
method of the present invention. More specifically, the desired
object can be achieved by heating the EG solution to a temperature
of at least saturation solubility so as to dissolve solutes
completely, cooling the solution to temperatures ranging from 15 to
30.degree. C., and keeping the solution within the temperature
range for at least 1 hour.
[0119] (Solid-Liquid Separation Step)
[0120] By subjecting a precipitate after the crystallization
treatment in the third method of the present invention to the
solid-liquid separation step described with respect to the first
method of the present invention, a filtered cake containing BHET as
a main component can be obtained. That is, the target filtered cake
can be obtained by subjecting the precipitate precipitated by
crystallization and containing BHET as a main component to
solid-liquid separation with the precipitate kept at
crystallization temperatures (15 to 30.degree. C.). The filtered
cake is formed into a melt solution so as to be subjected to the
subsequent step. It is preferred to heat the filtered cake at such
temperatures (e.g., 120.degree. C. or lower, more preferably 70 to
120.degree. C., particularly preferably 80 to 120.degree. C.) that
the filtered cake melts but side reactions hardly occur.
[0121] (Evaporation Step)
[0122] An evaporation step in the third method of the present
invention is carried out by use of the above filtered cake as a raw
material to be subjected to the evaporation step in accordance with
the method described with respect to the second method of the
present invention. That is, a melt solution of the above filtered
cake is charged into the first evaporator, and low-boiling-point
components are evaporated at a temperature of 130 to 170.degree. C.
and a pressure of 300 to 1,000 Pa so as to obtain a first melt
solution having a total content of EG and free DEG of 3 to 10 wt %.
The first melt solution is then charged into the second evaporator,
and low-boiling-point components are evaporated at a temperature of
130 to 170.degree. C. and a pressure of 50 to 250 Pa so as to
obtain a second melt solution having a total content of EG and free
DEG of not higher than 0.45 wt %. By such an evaporation step, the
desired object can be achieved.
[0123] (Molecular Distillation Step)
[0124] A molecular distillation step in the third method of the
present invention is carried out by use of the second melt solution
obtained in the above evaporation step in accordance with the
method described with respect to the second method of the present
invention. That is, the target object can be achieved by charging
the above second melt solution into the falling-thin-film type
molecular still and distilling the solution at a temperature of 180
to 220.degree. C. and a pressure of not higher than 25 Pa.
[0125] Thus, according to the present invention, high-quality
bis(2-hydroxyethyl)terephthalate can be obtained efficiently by
purifying crude bis(2-hydroxyethyl)terephthalate by the above
operation. Further, the purified bis(2-hydroxyethyl)terephthalate
of the present invention can be polymerized in the presence of a
polymerization catalyst so as to produce a polyethylene
terephthalate.
EXAMPLES
[0126] Hereinafter, the present invention will be further described
with reference to Examples. It is needless to say that the present
invention shall not be limited by Examples. Further, properties in
Examples were measured in the following manner.
[0127] 1. Separation of Components and Measurement of Amounts
Thereof
[0128] 5 mg of sample was dissolved in chloroform so as to prepare
about 1,000 ppm of solution, and a measurement was made by using an
ultraviolet visible spectrophotometer as a detector at a
measurement wavelength of 240 nm and a silica-60 column of 4.6
mm.sup.ID.times.250 mm.sup.L in high-performance liquid
chromatography (HPLC.) LC-6 of Shimadzu Corporation with a
temperature of 40.degree. C., a flow rate of 1.0 ml/min, an
injection rate of 5 .mu.l and dichloromethane/dioxane as a mobile
phase.
[0129] 2. Identification of Solution Components
[0130] An LC/MS measurement was made so as to identify peaks of
HPLC. The peaks were measured and identified under the same
conditions as described above by use of SX-102A of JEOL.
[0131] 3. Optical Density of Sample
[0132] 5 mg of sample was dissolved in methanol so as to prepare a
10 wt % methanol solution. The absorbance at 380 nm of this
solution was measured by means of UVmini-1240 (product of Shimadzu
Corporation) with a cell length of 10 mm and blanks zero-point
corrected by use of methanol.
[0133] 4. Electric Conductivity
[0134] Electric conductivity was measured continuously by use of
electric conductivity meter 873CC of FOX BOLO CO., LTD.
[0135] 5. Water Content
[0136] A water content was measured by use of an MK-SS type Karl
Fischer moisture meter manufactured by Kyoto Electronics
Manufacturing Co., Ltd.
[0137] 6. pH
[0138] The pH of an ethylene glycol solution having a solid content
at 80.degree. C. of 20 wt % was measured by "JISZ8802".
[0139] 7. Average Particle Diameter of Precipitate
[0140] The average particle diameter of a precipitate was measured
by use of SALD-200V ER of Shimadzu Corporation by diluting a
crystallization solution to 10 times with EG.
Example 1
[0141] (Preparation of Starting Material)
[0142] (Preliminary Depolymerization)
[0143] 57 kg of flakes with an average size of 8 mm.times.8 mm
which had been obtained by crushing and adjusting post-consumer PET
bottles (bottles made of a polyethylene terephthalate) mixed with
10 wt % of colored PET bottles and 25 kg of mixture of
bis(2-hydroxyethyl)terephthal- ate(BHET) and an oligomer thereof
were charged into an 800-liter autoclave equipped with a stirrer
and subjected to preliminary depolymerization under normal pressure
at 250.degree. C.
[0144] (Depolymerization)
[0145] Then, to the preliminary depolymerization product, 418 kg of
ethylene glycol (EG) and 0.23 kg of sodium hydroxide as a
depolymerization catalyst were added, and the depolymerization
reaction was further promoted at a pressure of 0.15 MPa and a
temperature of 220.degree. C. so as to obtain 500 kg of
depolymerization reaction solution.
[0146] (Removal of Solid Foreign Materials)
[0147] This solution was cooled to 180.degree. C., solid foreign
materials (caps, labels, and the like) which had not been
decomposed in the depolymerization reaction were removed by a
60-mesh line strainer, and the resulting solution was transported
to an 800-liter cooling bath.
[0148] (Decolorization Treatment)
[0149] The temperature of the reaction solution in the cooling bath
was lowered to 80.degree. C., and solid foreign materials such as
pigments and fine particles having a particle diameter of not
smaller than 1 .mu.m were removed by a cartridge filter. Then, the
reaction solution was passed through a decolorization column filled
with activated carbon (105 kg of "DIAHOPE008" of Mitsubishi
Chemical Corporation) at a space velocity of 0.57 hr.sup.-1 so as
to be decolorized.
[0150] (Cation Exchange Treatment)
[0151] Then, the resulting solution was passed through a
cation-removing column filled with a cation exchanger (25 liters of
cation exchange resin "AMBERLITE IR-120B" of Rohm & Haas Co.,
Ltd.) at a temperature of 80.degree. C. and a space velocity of 4.8
hr.sup.-1 so as to be subjected to a cation exchange treatment.
[0152] (Anion Exchange Treatment)
[0153] Thereafter, the resulting solution was passed through a
connected pipe within 30 seconds and then passed through an
anion-removing column filled with an anion exchanger (mixture of 30
liters of anion exchange resin "AMBERLITE IRA96SB" and 30 liters of
cation exchange resin "AMBERLITE IR-120B" of Rohm & Haas Co.,
Ltd.) at a temperature of 80.degree. C. and a space velocity of 2
hr.sup.-1 so as to be subjected to an anion exchange treatment.
Thereby, the deionization treatment was completed.
[0154] The pH of the reaction solution was 5.2 before the cation
exchange treatment, 1.8 after the cation exchange treatment, and
4.9 after the anion exchange treatment. Further, the electric
conductivity of the reaction solution was 537 .mu.S/cm before the
cation exchange treatment and 0.4 .mu.S/cm after the anion exchange
treatment. Further, the solid (solute) concentration of the
reaction solution after the anion exchange treatment was 19.5 wt %.
Further, the content of 2-hydroxyethyl[2-(2-hydr-
oxyethoxy)ethyl]terephthalate (DEG ester) in the solid (solute) of
the reaction solution was 4.0 wt %.
[0155] (Crystallization Step)
[0156] The above deionized solution was cooled in a crystallization
bath from 80.degree. C. to 25.degree. C. at a rate of 0.2.degree.
C./min and kept at 25.degree. C. for 5 hours so as to be
crystallized. The average particle diameter of a precipitate was 60
.mu.m.
[0157] (Solid-Liquid Separation Step)
[0158] Thereafter, the resulting solution was subjected to
solid-liquid separation by use of a filter press using a filter
fabric having an air permeability of 5
cm.sup.3/min.multidot.cm.sup.2 while kept at 25.degree. C. so as to
obtain 145 kg (recovery rate: 29 wt %) of cake containing 60 wt %
of crude BHET and 355 kg of (recovery rate: 71 wt %) of filtrate
having a solid content of 3.5 wt %. The content of DEG ester in the
cake was 1.8 wt %.
Example 2
[0159] (Preparation of Starting Material)
[0160] A starting material was prepared in the same manner as in
Example 1.
[0161] (Crystallization Step)
[0162] The crystallization step of Example 1 was repeated except
that the crystallization temperature was 15.degree. C. The average
particle diameter of a precipitate was 61 .mu.m.
[0163] (Solid-Liquid Separation Step)
[0164] A cake was obtained in the same manner as in Example 1.
[0165] As a result, 150 kg (recovery rate: 30 wt %) of the cake
containing 61 wt % of crude BHET and 350 kg of (recovery rate: 70
wt %) of filtrate having a solid content of 2.5 wt % were obtained.
The content of DEG ester in the cake was 2.3 wt %.
[0166] From these facts, an improvement in crystallization
efficiency can be generally expected by lowering the
crystallization temperature, and in the present invention as well,
the tendency can be seen in the solid contents in the filtrate and
cake. At the same time, it was also found that the content of DEG
ester which was a content other than BHET in the cake increased as
solubility to EG was lowered. From this result, it was disclosed
that to obtain BHET of higher purity, a higher crystallization
temperature is better as long as crystals of BHET could be
obtained.
Comparative Example 1
[0167] (Preparation of Starting Material)
[0168] A starting material was prepared in the same manner as in
Example 1.
[0169] (Crystallization Step)
[0170] A cake was obtained in the same manner as in Example 1
except that the crystallization temperature was 5.degree. C. The
average particle diameter of a precipitate was 62 .mu.m.
[0171] (Solid-Liquid Separation Step)
[0172] A cake was obtained in the same manner as in Example 1.
[0173] As a result, 155 kg (recovery rate: 31 wt %) of the cake
containing 62 wt % of crude BHET and 345 kg of (recovery rate: 71
wt %) of filtrate having a solid content of 1.7 wt % were obtained.
Although an effect caused by a decrease in the temperature was
clearly recognized in terms of contents, the content of DEG ester
in the cake reached 3.0 wt %.
Comparative Example 2
[0174] (Preparation of Starting Material)
[0175] A starting material was prepared in the same manner as in
Example 1.
[0176] (Crystallization Step)
[0177] The crystallization step of Example 1 was repeated except
that the crystallization temperature was 35.degree. C. As a result,
a satisfactory crystallization result could not be obtained, the
content of solids in a filtrate reached 7 wt %, and the subsequent
step could not be carried out.
[0178] Table 1 shows the yields of solids and the contents of DEG
esters in the crystallization steps of Examples 1 and 2 and
Comparative Example 1.
2 TABLE 1 Properties of Conditions Crystallization for Crystal-
Solution lization Properties of Cake Content of DEG Temperature
Recovery Rate Solid Content Content of DEG Component (wt %)
(.degree. C.) (wt %) (wt %) Component (wt %) Ex. 1 4.0 25 29 60 1.8
Ex. 2 4.0 15 30 61 2.3 C. Ex. 1 4.0 05 31 62 3.0 Properties of
Filtrate Total Solid Recovery Rate Solid Content Content (wt %) (wt
%) (wt %) Ex. 1 71 3.5 19.9 Ex. 2 70 2.5 20.1 C. Ex. 1 69 1.7 20.0
Ex.: Example, C. Ex.: Comparative Example
Example 3
[0179] (Preparation of Starting Material)
[0180] A starting material was prepared in the same manner as in
Example 1. The obtained deionized solution was used as a starting
material for purification in the evaporation steps shown in FIG.
1.
[0181] (First Evaporation Step)
[0182] The starting material was fed to the first falling-thin-film
type evaporator at a feed rate of 138 kg/hr so as to evaporate
low-boiling-point components at a temperature of 150.degree. C. and
a pressure of 500 Pa. The evaporation treatment time was 3.6 hours.
The amount of a first condensate produced by cooling the
low-boiling-point components was 109kg/hr. The amount of a produced
first melt solution was 29 kg/hr.
[0183] The total content of EG and free DEG and the content of an
oligomer in the first melt solution are shown in Table 2.
[0184] (Second Evaporation Step)
[0185] Then, the first melt solution was fed to the second
falling-thin-film type evaporator at a feed rate of 29 kg/hr so as
to evaporate remaining low-boiling-point components at a
temperature of 150.degree. C. and a pressure of 80 Pa. The
evaporation treatment time was 3.7 hours. The amount of a second
condensate produced by cooling the low-boiling-point components was
2 kg/hr. The amount of a produced second melt solution was 27
kg/hr.
[0186] The content of free DEG in the first and second condensates
and the second melt solution, and the total content of EG and free
DEG and the content of an oligomer in the second melt solution are
shown in Table 2.
[0187] (Molecular Distillation Step)
[0188] The second melt solution was fed to the falling-thin-film
type molecular still at a feed rate of 27 kg/hr, and molecular
distillation was carried out at a temperature of 195.degree. C. and
a pressure of 13 Pa so as to distill out a fraction such that the
weight ratio of the fraction to a distillation pot residue became
7:3. The fraction was distilled out at a rate of 19 kg/hr, and time
required by the distillation was 3.7 hours. In the molecular
distillation, the whole amount of the first condensate obtained in
the first evaporation step was used as a portion of a cooling
medium for the internal condenser. The results of analysis of the
obtained fraction are shown in Table 3.
Example 4
[0189] (Preparation of Starting Material)
[0190] A starting material was prepared in the same manner as in
Example 1.
[0191] (Crystallization Step)
[0192] A crystallization step was carried out in the same manner as
in Example 1. The obtained cake was heated and molten in a nitrogen
atmosphere at 100.degree. C. and used as a starting material for
purification in the distillation step shown in FIG. 1.
[0193] (First Evaporation Step)
[0194] The starting material was fed to the first falling-thin-film
type evaporator at a feed rate of 50 kg/hr so as to evaporate
low-boiling-point components at a temperature of 150.degree. C. and
a pressure of 500 Pa. The evaporation treatment time was 2.9 hours.
The amount of a first condensate produced by cooling the
low-boiling-point components was 18 kg/hr. The amount of a produced
first melt solution was 32 kg/hr.
[0195] The total content of EG and free DEG and the content of an
oligomer in the first melt solution are shown in Table 2.
[0196] (Second Evaporation Step)
[0197] Then, the first melt solution was fed to the second
falling-thin-film type evaporator at a feed rate of 32 kg/hr so as
to evaporate remaining low-boiling-point components at a
temperature of 150.degree. C. and a pressure of 80 Pa. The
evaporation treatment time was 2.9 hours. The amount of a second
condensate produced by cooling the low-boiling-point components was
2 kg/hr. The amount of a produced second melt solution was 30
kg/hr.
[0198] The content of free DEG in the first and second condensates
and the second melt solution, and the total content of EG and free
DEG and the content of an oligomer in the second melt solution are
shown in Table 2.
[0199] (Molecular Distillation Step)
[0200] The second melt solution was fed to the falling-thin-film
type molecular still at a feed rate of 30 kg/hr, and molecular
distillation was carried out at a temperature of 195.degree. C. and
a pressure of 13 Pa so as to distill out a fraction such that the
weight ratio of the fraction to a distillation pot residue became
7:3. The fraction was distilled out at a rate of 21 kg/hr, and time
required by the distillation was 2.9 hours. The results of analysis
of the obtained fraction are shown in Table 3.
Comparative Example 3
[0201] (Preparation of Starting Material)
[0202] A starting material was prepared in the same manner as in
Example 1.
[0203] (Evaporation Step)
[0204] A first evaporation step was carried out in the following
manner, and a second evaporation step was not carried out. That is,
the starting material was fed to the evaporator at a feed rate of
25 kg/hr so as to evaporate low-boiling-point components at a
temperature of 150.degree. C. and a pressure of 500 Pa. The
evaporation treatment time was 20 hours. The amount of a condensate
produced by cooling the low-boiling-point components was 20 kg/hr.
The amount of a produced melt solution was 5 kg/hr.
[0205] The content of free DEG in the first condensate and the
first melt solution, and the total content of EG and free DEG and
the content of an oligomer in the first melt solution are shown in
Table 2.
[0206] (Molecular Distillation Step)
[0207] The first melt solution obtained by the above procedure was
fed to the falling-thin-film type molecular still at a feed rate of
5 kg/hr, and molecular distillation was carried out at a
temperature of 190.degree. C. and a pressure of 13 Pa so as to
distill out a fraction such that the weight ratio of the fraction
to a distillation pot residue became 7:3. The fraction was
distilled out at a rate of 3.5 kg/hr, and time required by the
distillation was 20.1 hours. The results of analysis of the
obtained fraction are shown in Table 3.
[0208] As can be understood from Table 3, the evaporation treatment
was carried out only in the first evaporator and evaporation of the
solvents was performed for a long time in the presence of a large
amount of EG which was a low-boiling-point component, the content
of DEG ester in the fraction was 1.9 wt %.
Comparative Example 4
[0209] (Preparation of Starting Material)
[0210] A starting material was prepared in the same manner as in
Example 1.
[0211] (Evaporation Step)
[0212] A first evaporation step was carried out in the same manner
as in Example 1, and a second evaporation step was not carried
out.
[0213] The content of free DEG in the first condensate and the
first melt solution, and the total content of EG and free DEG and
the content of an oligomer in the first melt solution are shown in
Table 2.
[0214] (Molecular Distillation Step)
[0215] The first melt solution obtained by the above procedure was
fed to the falling-thin-film type molecular still at a feed rate of
29 kg/hr, and molecular distillation was carried out at a
temperature of 197.degree. C. and a pressure of 13 Pa so as to
distill out a fraction such that the weight ratio of the fraction
to a distillation pot residue became 7:3. The fraction was
distilled out at a rate of 20.3 kg/hr, and time required by the
distillation was 3.6 hours. The results of analysis of the obtained
fraction are shown in Table 3.
[0216] In Comparative Example 4, the molecular distillation
treatment was carried out with 5.1 wt % of low-boiling-point
components remaining.. Accordingly, solutes such as BHET entrained
evaporated solvents and stuck on the internal wall of the condenser
situated before the vacuum means, thereby making it difficult to
perform a stable molecular distillation operation.
3TABLE 2 Results of Analysis of Condensates and Melt Solutions in
Evaporation Steps Ex. 3 Ex. 4 C. Ex. 3 C. Ex. 4 Content of Free DEG
in Condensate(s) and Melt 1.4 1.2 3.1 1.4 Solution in Evaporation
Steps (wt %).sup.1) Content of EG and Free DEG in First Melt
Solution (wt %) 5.1 5.1 0.4 5.1 Content of Oligomer in First Melt
Solution (wt %) 11.1 11.1 20.4 11.1 Content of EG and Free DEG in
Second Melt Solution (wt %) 0.3 0.3 -- -- Content of Oligomer in
Second Melt Solution (wt %) 12.0 12.0 -- -- Ex.: Example, C. Ex.:
Comparative Example .sup.1)Example 3 . . . Content of Free DEG in
First and Second Condensates and Second Melt Solution Comparative
Examples 3 and 4 . . . Content of Free DEG in First Condensate and
First Melt Solution DEG: diethylene glycol EG: ethylene glycol
[0217]
4TABLE 3 Results of Analysis of Fractions by Molecular Distillation
Quality of Purified BHET after Molecular Distillation Ex. 3 Ex. 4
C. Ex. 3 C. Ex. 4 Yield of Purified BHET (kg) 70 61 70 61 Optical
Density (380 nm) 0.002 0.000 0.005 0.007 Content of BHET (wt %)
99.0 99.2 96.8 97.0 Content of DEG Ester (wt %) 0.7 0.5 1.9 2.5
Content of Oligomer (wt %) 0.2 0.2 1.2 0.3 Others (wt %) 0.1 0.1
0.1 0.2 Ex.: Example, C. Ex.: Comparative Example BHET . . .
bis(2-hydroxyethyl)terephthalate DEG ester . . .
2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate MHET . . .
mono(2-hydroxyethyl)terephthalate
Comparative Examples 5 to 12
[0218] (Preparation of Starting Material)
[0219] Starting materials were prepared in the same manner as in
Example 1.
[0220] (First Evaporation Step)
[0221] The starting materials were fed to the first
falling-thin-film type evaporator, and low-boiling-point components
were evaporated under evaporation conditions of Table 4 such that
the total contents of EG and free DEG in first melt solutions
became 5 wt %.
5 TABLE 4 C. Ex. 5 6 7 8 9 10 11 12 Tem- 120 120 120 180 180 180
150 150 perature (.degree. C.) Pressure 200 500 2000 200 500 2000
200 2000 (Pa) Evapo- 4.0 4.6 5.5 2.8 3.2 3.9 3.2 4.3 ration Time
(hr) C. Ex.: Comparative Example
[0222] The total contents of EG and free DEG and the contents of
oligomers in the first melt solutions are shown in Table 5.
[0223] (Second Evaporation Step)
[0224] A second evaporation step was carried out in the same manner
as in Example 3. The contents of free DEG in the first and second
condensates and the second melt solutions, and the total contents
of EG and free DEG and the contents of oligomers in the second melt
solutions are shown in Table 5.
[0225] (Molecular Distillation Step)
[0226] The second melt solutions obtained by the above procedure
were fed to the falling-thin-film type molecular still, and
fractions were distilled out such that the weight ratio of the
fraction to a distillation pot residue became 7:3. The results of
analysis of the obtained fractions are shown in Table 6.
[0227] In Comparative Examples 5 to 12, the first evaporation step
was carried out under various evaporation conditions. It is seen
that in all cases, some influence was exerted on the quality or
yield of purified BHET.
6TABLE 5 Results of Analysis of Condensates and Melt Solutions in
Evaporation Step C. Ex. 5 C. Ex. 6 C. Ex. 7 C. Ex. 8 C. Ex. 9 C.
Ex. 10 C. Ex. 11 C. Ex. 12 Content of Free DEG in First and Second
2.1 2.2 2.3 1.9 2.3 5.0 1.4 2.9 Condensates and Second Melt
Solution (wt %) Content of EG and Free DEG in First Melt 5.0 5.0
5.0 5.0 5.0 5.0 5.0 5.0 Solution (wt %) Content of Oligomer in
First Melt 14.2 15.0 16.3 10.1 10.7 12.2 10.8 15.1 Solution (wt %)
Content of EG and Free DEG in Second Melt 0.3 0.3 0.3 0.3 0.3 0.3
0.3 0.3 Solution (wt %) Content of Oligomer in Second Melt 15.1
15.9 17.2 11.0 11.6 13.1 11.7 16.0 Solution (wt %) C. Ex.:
Comparative Example
[0228]
7TABLE 6 Results of Analysis of Fractions by Molecular Distillation
Quality of Purified BHET after Molecular Distillation C. Ex. 5 C.
Ex. 6 C. Ex. 7 C. Ex. 8 C. Ex. 9 C. Ex. 10 C. Ex. 11 C. Ex. 12
Yield of Purified BHET (kg) 68 70 70 50 66 70 63 70 Optical Density
(380 nm) 0.005 0.005 0.006 0.004 0.006 0.008 0.003 0.007 Content of
BHET (wt %) 97.0 96.9 96.6 98.1 97.3 96.6 98.7 96.2 Content of DEG
Ester (wt %) 1.8 1.8 1.9 1.1 1.9 2.8 0.7 2.5 Content of Oligomer
(wt %) 1.1 1.1 1.2 0.2 0.2 0.4 0.2 1.2 Others (wt %) 0.1 0.2 0.1
0.4 0.4 0.2 0.4 0.1 C. Ex.: Comparative Example
Comparative Examples 13 to 20
[0229] (Preparation of Starting Material)
[0230] Starting materials were prepared in the same manner as in
Example 1.
[0231] (First Evaporation Step)
[0232] A first evaporation step was carried out in the same manner
as in Example 3.
[0233] (Second Evaporation Step)
[0234] First melt solutions were fed to the second
falling-thin-film type evaporator, and low-boiling-point components
were evaporated under evaporation conditions of Table 7 such that
the total contents of EG and free DEG in second melt solutions
became 0.3 wt %.
8 TABLE 7 C. Ex. 13 14 15 16 17 18 19 20 Temperature 120 120 120
180 180 180 150 150 (.degree. C.) Pressure (Pa) 40 80 300 40 80 300
40 300 Evaporation 4.2 4.7 5.6 2.9 3.3 4.1 3.4 4.4 Time (hr) C.
Ex.: Comparative Example
[0235] The contents of free DEG in the first and second condensates
and the second melt solutions, and the total contents of EG and
free DEG and the contents of oligomers in the second melt solutions
are shown in Table 8.
[0236] (Molecular Distillation Step)
[0237] The second melt solutions obtained by the above procedure
were fed to the falling-thin-film type molecular still, and
fractions were distilled out such that the weight ratio of the
fraction to a distillation pot residue became 7:3. The results of
analysis of the obtained fractions are shown in Table 9.
[0238] In Comparative Examples 13 to 20, the second evaporation
step was carried out under various evaporation conditions. It is
seen that in all cases, some influence was exerted on the quality
or yield of purified BHET, as in the case of Comparative Examples 5
to 12.
9TABLE 8 Results of Analysis of Condensates and Melt Solutions in
Evaporation Steps C. Ex. 13 C. Ex. 14 C. Ex. 15 C. Ex. 16 C. Ex. 17
C. Ex. 18 C. Ex. 19 C. Ex. 20 Content of Free DEG in 1.9 2.0 2.1
1.7 2.1 2.9 1.2 2.4 First and Second Condensates and Second Melt
Solution (wt %) Content of EG and Free DEG 5.1 5.1 5.1 5.1 5.1 5.1
5.1 5.1 in First Melt Solution (wt %) Content of Oligomer in 11.1
11.1 11.1 11.1 11.1 11.1 11.1 11.1 First Melt Solution (wt %)
Content of EG and Free DEG 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 in
Second Melt Solution (wt %) Content of Oligomer in 14.4 15.2 16.5
11.7 12.0 13.5 11.0 15.3 Second Melt Solution (wt %) C. Ex.:
Comparative Example
[0239]
10TABLE 9 Results of Analysis of Fractions by Molecular
Distillation Quality of Purified BHET after Molecular Distillation
C. Ex. 13 C. Ex. 14 C. Ex. 15 C. Ex. 16 C. Ex. 17 C. Ex. 18 C. Ex.
19 C. Ex. 20 Yield of Purified BHET (kg) 69 70 70 67 69 70 68 70
Optical Density (380 nm) 0.004 0.004 0.005 0.003 0.005 0.007 0.003
0.006 Content of BHET (wt %) 97.6 97.6 97.0 98.3 97.6 96.9 98.8
97.3 Content of DEG Ester (wt %) 1.5 1.5 1.8 1.0 1.8 2.3 0.7 1.9
Content of Oligomer (wt %) 0.5 0.6 1.1 0.2 0.2 0.4 0.2 0.6 Others
(wt %) 0.4 0.3 0.1 0.5 0.4 0.4 0.3 0.2 C. Ex.: Comparative
Example
Example 5
[0240] (Preparation of Starting Material)
[0241] 202 kg of crushed flakes of post-consumer PET bottles were
preliminarily depolymerized by 118 kg of mixture of BHET and an
oligomer thereof under heating at 280.degree. C. Then, 0.96 kg of
sodium hydroxide as a depolymerization catalyst and 1,800 kg of EG
were added to the preliminary depolymerization product such that
the concentration of crude BHET in a depolymerization solution
became 20 wt %, and depolymerization was further promoted under
heating at 220.degree. C. so as to obtain 2,120 kg of the
depolymerization solution containing EG as a solvent.
[0242] The temperature of this depolymerization solution was
lowered to 80.degree. C., foreign materials and impurities
contained were removed in accordance with a known method, the
resulting solution was cooled to 25.degree. C., crystallization of
BHET was conducted for 5 hours, and slurry containing BHET crystals
and EG as a solvent was subjected to a filter press so as to carry
out solid-liquid separation. Thereby, 770 kg of crude BHET crystal
cake containing 45 wt % of EG was obtained.
[0243] The cake obtained by the above procedure was heated to
100.degree. C. in a nitrogen atmosphere so as to be molten and used
as a starting material for purification in the evaporation steps
shown in FIG. 1. The total concentration of solutes in this
starting material was 19.5 wt %. The starting material contained
4.0 wt % of DEG ester based on all solutes and had an electric
conductivity of 0.4 .mu.S/cm.
[0244] (First Evaporation Step)
[0245] The starting material was fed to the first falling-thin-film
type evaporator at a feed rate of 50 kg/hr so as to evaporate
low-boiling-point components at a temperature of 150.degree. C. and
a pressure of 500 Pa. The evaporation treatment time was 15.4
hours. The amount of a first condensate produced by cooling the
low-boiling-point components was 21 kg/hr. The amount of a produced
first melt solution was 29 kg/hr.
[0246] The total content of EG and free DEG and the content of an
oligomer in the first melt solution are shown in Table 10.
[0247] (Second Evaporation Step)
[0248] Then, the first melt solution was fed to the second
falling-thin-film type evaporator at a feed rate of 29 kg/hr so as
to evaporate remaining low-boiling-point components at a
temperature of 150.degree. C. and a pressure of 80 Pa. The
evaporation treatment time was 15.9 hours. The amount of a second
condensate produced by cooling the low-boiling-point components was
2 kg/hr. The amount of a produced second melt solution was 27
kg/hr.
[0249] The content of free DEG in the first and second condensates
and the second melt solution, and the total content of EG and free
DEG and the content of an oligomer in the second melt solution are
shown in Table 10.
[0250] (Molecular Distillation Step)
[0251] The second melt solution was fed to the falling-thin-film
type molecular still at a feed rate of 27 kg/hr, and molecular
distillation was carried out at a temperature of 195.degree. C. and
a pressure of 13 Pa so as to distill out a fraction such that the
weight ratio of the fraction to a distillation pot residue became
7:3. The fraction was distilled out at a rate of 19 kg/hr, and time
required by the distillation was 15.7 hours. In the molecular
distillation, the whole amount of the first condensate obtained in
the first evaporation step was used as a portion of a cooling
medium for the internal condenser. The results of analysis of the
obtained fraction are shown in Table 11.
11TABLE 10 Results of Analysis of Condensates and Melt Solutions in
Evaporation Steps Example 5 Content of Free DEG in Condensates and
Melt Solution in 1.3 Evaporation Steps (wt %) Content of EG and
Free DEG in First Melt Solution (wt %) 5.1 Content of Oligomer in
First Melt Solution (wt %) 11.1 Content of EG and Free DEG in
Second Melt Solution (wt %) 0.3 Content of Oligomer in Second Melt
Solution (wt %) 12.0
[0252]
12TABLE 11 Results of Analysis of Fraction by Molecular
Distillation Quality of Purified BHET after Molecular Distillation
Example 5 Yield of Purified BHET (kg) 296 Optical Density (380 nm)
0.000 Content of BHET (wt %) 99.2 Content of DEG Ester (wt %) 0.5
Content of Oligomer (wt %) 0.2 Others (wt %) 0.1
Example 6
[0253] (Preparation of Starting Material)
[0254] (Preliminary Depolymerization)
[0255] 57 kg of flakes with an average size of 8 mm.times.8 mm
which had been obtained by crushing and adjusting post-consumer PET
bottles (bottles made of a polyethylene terephthalate) mixed with
10 wt % of multilayered colored PET bottles for beers which
contained a polymethaxylylene adipamide (Nylon MXD6) as a gas
barrier agent and 25 kg of BHET were charged into an 800-liter
autoclave equipped with a stirrer and subjected to preliminary
depolymerization under heating at normal pressure and a temperature
of 250.degree. C.
[0256] (Depolymerization)
[0257] Then, to the preliminary depolymerization product, 418 kg of
EG and 0.23 kg of sodium hydroxide as a depolymerization catalyst
were added, and the depolymerization was further promoted at a
pressure of 0.13 MPa and a temperature of 220.degree. C. The
depolymerization was carried out for 60 minutes with
low-boiling-point components such as water distilled off from the
top of a rectification column placed on the autoclave so as to
obtain 500 kg of depolymerization reaction solution containing EG
as a solvent.
[0258] (Removal of Solid Foreign Materials)
[0259] The reaction solution was cooled to 180.degree. C.,
undecomposed solid foreign materials (caps, labels, and the like)
contained in the reaction solution were removed by use of a 60-mesh
line strainer, and the resulting solution was transported to an
800-liter cooling bath.
[0260] (Decolorization Treatment)
[0261] The solution in the cooling bath was cooled to 80.degree.
C., and foreign materials such as pigments and fine particles
having a particle diameter of not smaller than 1 .mu.m were removed
by a filter. Then, the depolymerization reaction solution was
passed through a decolorization column filled with activated carbon
(105 kg of "DIAHOPE008" of Mitsubishi Chemical Corporation) at a
temperature of 80.degree. C. and a space velocity of 0.57
hr.sup.-1, and foreign materials such as fine particles and fine
carbon powder having a particle diameter of not smaller than 1
.mu.m were then removed by a filter.
[0262] (Cation Exchange Treatment)
[0263] Then, the reaction solution was passed through a
cation-removing column filled with a cation exchanger (25 liters of
cation exchange resin "AMBERLITE IR-120B" of Rohm & Haas Co.,
Ltd.) at a temperature of 80.degree. C. and a space velocity of 4.8
hr.sup.-1 so as to be subjected to a cation exchange treatment.
[0264] (Anion Exchange Treatment)
[0265] Thereafter, the resulting solution was passed through a
connected pipe within 30 seconds and then passed through an
anion-removing column filled with an anion exchanger (mixture of 30
liters of anion exchange resin "AMBERLITE IRA96SB" and 30 liters of
cation exchange resin "AMBERLITE IR-120B" of Rohm & Haas Co.,
Ltd.) at a temperature of 80.degree. C. and a space velocity of 2
hr.sup.-1 so as to be subjected to an anion exchange treatment.
Thereby, the deionization treatment was completed.
[0266] The pH of the reaction solution was 5.2 before the cation
exchange treatment, 1.8 after the cation exchange treatment, and
4.9 after the anion exchange treatment. The electric conductivity
of the reaction solution was 537 .mu.S/cm before the cation
exchange treatment and 0.4 .mu.S/cm after the anion exchange
treatment. Further, the total content of solutes in the reaction
solution after the anion exchange treatment was 19.5 wt %, and the
content of DEG ester based on all solutes was 4.0 wt %. Further,
the content of a gas barrier agent component (component derived
from Nylon MXD6) in the solid (solute) was 0.6 wt %.
[0267] (Crystallization Step)
[0268] The above deionized solution was cooled in a crystallization
bath from 80.degree. C. to 25.degree. C. at a rate of 0.2.degree.
C./min and kept at 25.degree. C. for 5 hours so as to be
crystallized. The average particle diameter of obtained crystals
was 60 .mu.m.
[0269] (Solid-Liquid Separation Step)
[0270] Thereafter, the resulting solution was subjected to
solid-liquid separation at 25.degree. C. by use of a filter press
using a filter fabric having an air permeability of 5
cm.sup.3/min.multidot.cm.sup.2 so as to obtain 145 kg (recovery
rate: 29 wt %) of cake containing 60 wt % of crude BHET. The
content of the gas barrier agent component in the cake was 0.1 wt
%. The cake obtained by this procedure was heated to 10.degree. C.
and molten in a nitrogen atmosphere and used as a starting material
for purification in the distillation steps shown in FIG. 1.
[0271] (First Evaporation Step)
[0272] The starting material was fed to the first falling-thin-film
type evaporator at a feed rate of 50 kg/hr so as to evaporate
low-boiling-point components at a temperature of 150.degree. C. and
a pressure of 500 Pa. The evaporation treatment time was 15.4
hours. The amount of a first condensate produced by cooling the
low-boiling-point components was 21 kg/hr. The amount of a produced
first melt solution was 29 kg/hr. The total content of EG and free
DEG in the first melt solution was 5.0 wt %.
[0273] (Second Evaporation Step)
[0274] Then, the first melt solution was fed to the second
falling-thin-film type evaporator at a feed rate of 29 kg/hr so as
to evaporate remaining low-boiling-point components at a
temperature of 150.degree. C. and a pressure of 80 Pa. The
evaporation treatment time was 15.9 hours. The amount of a second
condensate produced by cooling the low-boiling-point components was
2 kg/hr. The amount of a produced second melt solution was 27
kg/hr. The total content of EG and free DEG in the second melt
solution was 0.3 wt %.
[0275] (Molecular Distillation Step)
[0276] The second melt solution was fed to the falling-thin-film
type molecular still at a feed rate of 27 kg/hr, and molecular
distillation was carried out at a temperature of 195.degree. C. and
a pressure of 13 Pa so as to distill out a fraction such that the
weight ratio of the fraction to a distillation pot residue became
7:3. The fraction was distilled out at a rate of 19 kg/hr, and time
required by the distillation was 15.7 hours. The results of
analysis of the obtained fraction are shown in Table 12.
[0277] The optical density at 380 nm of the obtained purified BHET
was 0.002, and components derived from the gas barrier polymer were
not detected. From this result, it was found that even colored PET
bottles having a gas barrier property can be recycled by using the
method of the present invention.
13TABLE 12 Results of Analysis of Fraction by Molecular
Distillation Quality of Purified BHET after Molecular Distillation
Example 6 Yield of Purified BHET (kg) 61 Optical Density (380 nm)
0.002 Content of BHET (wt %) 99.0 Content of DEG Ester (wt %) 0.6
Content of Oligomer (wt %) 0.2 Others (wt %) 0.2 Gas Barrier Agent
Component (wt %) Not Detected
[0278] Effect of the Invention
[0279] As described above, according to the present invention,
high-purity BHET can be obtained from an ethylene glycol solution
containing crude bis(2-hydroxyethyl)terephthalate, particularly a
decomposition product solution (EG solution) which is obtained by
decomposing a polyester containing a polyethylene terephthalate as
a main component by use of EG and contains
bis(2-hydroxyethyl)terephthalate as a main solute and ethylene
glycol as a main solvent, while minimizing by-production of
impurity components, particularly DEG, DEG ester and an oligomer,
during a purification process and by separating a gas barrier agent
component as well as these impurity components efficiently.
[0280] Possibility of Industrial Utilization
[0281] The purification methods of the present invention are useful
in a so-called "material recycle" field in which polyethylene
terephthalate molded articles, particularly polyethylene
terephthalate bottles, are collected and reused.
* * * * *